I'm doing a full teardown / playfield swap on a customer's Medusa, and ran into a few issues finding appropriate stand-up targets for the multi-morphic (upper) drop target unit and the zipper flippers. Hopefully this info will help others.
As seems to be common for many Medusas the stand-up translucent targets behind the upper drop target assembly were replaced in the past when the target faces broke. No one appears to sell the exact switch assembly, but you can use a Bally ASE-2911-62 switch (available from PBR and perhaps Marco) and replace the blue plastic target arm with one of the new translucent target arms from http://www.langelius.com/ - these are an exact match for the originals. You'll have to remove the new -62 switch from the supplied mounting bracket, replace the existing blue target arm with the translucent one, and mount the switch (using the black #5 screws from the new -62 switch) to the rear of the drop target assembly. The new switch comes with the appropriate diode and capacitor. Completed view below.
The zipper flipper unit uses pairs of 1" OD-3/8" ID nylon washers and a single 5/8" OD-5/16" ID nylon washer (both 1/32" thick) as bearing surfaces for the movable flipper base plates; none of the pinball parts suppliers stock these. A keystone 3147 is a perfect match for the 1" OD washers; you can find these at Mouser(.com). The best match I could find for the 5/8" OD washer was a 3/4" OD - 21/64" ID washer on eBay; the larger OD fits with no issues. I opted to use a second one of these nylon washers under the large flat washer to eliminate any metal-to-metal contact. (I had to buy a bag of 100 but they weren't all that expensive.) The new washers take a lot of "slop" out of the movable flipper base plates.
The end-of-stroke switches on the upper flippers are a special breed used only on Medusa. The upper left uses a paired ASW-A20-13 and ASW-A20-37, while the upper right uses a paired ASW-A20-12 and ASW-A20-36. The -36/-37 have an attached nylon switch lifter; all four switches are high current varieties. The inner EOS switches power to the lights beneath the playfield under the lower flipper inserts, while the outer EOS switches high power to the flipper coil. The BFLIP-01 kit sold by PBR supplies an EOS that isn't really a good match for the -12/-13 switches; it can be made to work by shortening the longer (movable) blade. The good news is that you can purchase the -13, -36, and -37 switches from PBR; the -12 switch is not available. If you get an extra -13 switch you can disassemble it and add some side lug solder plates to make an acceptable substitute. I'll add a picture of the zipper flipper unit shortly.

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Added over 8 years ago: Added info regarding the upper flipper end-of-stroke switches:

The -12 switches supplied by PBR aren't a good replacement for the originals; the movable blade on those switches is not long enough to fully reach the insulator. I was able to use the EOS switches in the PBR BFLIP01 kit (DE-180-5018) by cutting the movable blade one position shorter; the resulting switch stack is built from the DE-180-5018 (inner) and -36 (or -37) switch (outer).

(Please help out Jim Heck who did the artwork for the reproduction Medusa playfields.)

I'm doing a playfield swap for Jim using one of the CPR reproduction Medusa playfields. I have a question about how the flipper bat assemblies for the zipper flipper were originally installed. When Jim dropped off his original playfield he had already removed all topside components prior to running the playfield through a Cruse scanner, and the pictures he took don't have quite enough detail to be sure of the proper assembly order.

In one picture Jim took it appears a 3/4-inch diameter thick metal washer is installed between the flipper bat and the playfield. This seems reasonable, since something is needed to keep the flipper bat raised slightly above the playfield (otherwise the flipper pawl would just drop downward and pull the flipper bat with it causing the flipper bat to scrape on the playfield). However, it seems to me the metal washer would itself cause wear on the top surface of the playfield as the zipper flipper unit moves the flipper bats inward and outward.

Is this really how Bally assembled, the game? I could see Bally using a metal collar with a set screw installed on the flipper shaft, resting atop the flipper bushing, to limit any downward movement of the flipper bat. The large flat washer seems like a hack - and this game has several of them. If the washer was the factory method I'll add a thin nylon washer below it to help protect the new playfield.

Any details regarding how the flipper bat assemblies are installed on your game would be greatly appreciated!

Has anyone installing the CPR reproduction playfield run into issues with fitting the "feature display assembly" (the long metal and plastic assembly with a bunch of lights behind and above the top drop target assembly) into place? The 9/16" thickness of the CPR playfield (compared to the original playfield ~1/2" thickness) coupled with the height of the playfield side and rear rails doesn't accommodate the space between the top and bottom edges of the metal bracket that makes up the feature display assembly. It looks like I'll either have to route out a recess on the bottom edge of the playfield to accommodate the ends of the bracket or trim the rear playfield rail - although I don't know if the display will bump up against the playfield posts, so the latter may not work.

I opted to route out 1" x 4" x 1/16" deep recesses on the bottom of the playfield for the feature display assembly mounting bracket to allow it to fit properly with the CPR reproduction playfield. I'd recommend this to anyone doing a Medusa playfield - preferably BEFORE you do any assembly - so the feature display doesn't get pushed upward by the playfield side rails.

Looking back I wondered why the pop bumper mounting recesses were deeper on the CPR reproduction than the original - that should have sent up a red flag or three. Ah well ...

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The multi-morphic drop target assembly used on some Bally games is a really neat piece of engineering. It has the usual reset coil (2 coils in the case of the upper drop target unit on Medusa) to reset all the targets so they are above the playfield, but each target also has a coil associated with it that can be operated by the game software to drop that target below the playfield (as if a ball hit it). If you watch the drop targets carefully when they are reset at the start of a ball, all targets will be above the playfield briefly, then the 3 outer targets on each side of the #4 target will quickly drop, leaving only the center (#4) target above the playfield.

If your #2 target is not dropping it could be due to a bad "drop" coil for that target, a bad driver transistor for that coil, or broken wiring as the most likely causes. Use the game diagnostics solenoid test function to listen for the #2 target drop coil clicking as the game cycles through the solenoids (solenoid number 4 is associated with the #2 drop target). (Page 13 of the game manual, available via www.ipdb.org, describes how to use the game diagnostics.)

Post #388 is your friend: it has details on how to assemble the custom EOS switches from stock parts (no one sells the complete unit).

Check VERY carefully, but I'm nearly 100% certain the outer-most terminal on the switch assembly - the one nearest the screw heads that hold the switch stack in place - is just a tie point for the black/yellow (one flipper) and red/black (other flipper) wires coming from the wiring harness to the zipper flipper assembly and then on to one lug of the flipper coil. I suspect it was wired that way by the factory to allow the wires from the harness to move together.

If I'm correct all you need to do is connect together the wires leading to that old "fifth" lug, solder, and insulate.