Not a lot of play time in but so far I like it. Should make the game more approachable to others since the top playfield flipper is also controlled by the lower buttons now. Don't know if this will cause excessive wear but I think for my home environment it should be fine. I may add a switch to go back to 'as designed' if needed.
Here are the details to the mod (soldering required). Components were parts I had lying around (except for the nylon washers).
a) Long blades on top and middle.
b) Black wire on center blade so it makes good contact with either switch.
c) Red wire on top blade.
d) Gold contacts facing each other for top and middle blades (lower flipper)
e) Bottom blade connected with wire to White button blade with white wire.
f) Add spacer to bottom of other switches to match the height of the red switch.
g) Double sided tape or adhesive to add nylon washer to button board.
h) The modified box extends slightly into the cabinet.
i) No adjustment of the blades was needed and the amount of separation between the stages seems good.
*The backside of the gold contact on the middle blade making contact with the lower blade's contact is not ideal, but wanted to give the two stage flipper a try before modifying or buying a part like below.
two contact leaf (resized).png
1) 2x long blade from new slingshot switch to add the second stage switch
2) 2x spacer scavenged from old leaf switches to match white and yellow switch heights to red switch height.
3) 2x very thin spacer scavenged from old leaf switches to cover added blade (reduces nut height)
3) 6x 1.5mm x 8.2mm (OD) as measured, nylon washers to account for additional switch heights when mounting switch board to button box.
4) 2x short wires
Time: about 1hr for the first box to figure things out, 20 minutes for the second box.