Bally did apply a thin layer of protection on their playfields called "Tuffcoat". This coating is nowhere near as robust as Diamondplate and seemed to wear very quickly. I have done NOS playfield swaps on games coated with Tuffcoat and started to see some slight wear after only a couple thousand plays. So, you can expect the same thing after removing the mylar. Novus won't provide any protection, but wax will help quite a bit, though it does track itself everywhere.

Best bet is to find another playfield and swap the old one out. A thin layer of modern clearcoat will solve any future wear problems.

There are differences, even in the earlier cabinets.

For example, Evel Knievel has the backglass door on hinges. Most of the earlier cabinets will be the same except for the ones with chime boxes vs a sound board. I think the physical wood pieces are the same, but the harnesses would have some differences. Most of the early Bally cabinets from 1977-1980 are real close with the above exceptions. More differences with the switch to the -54 power supply as the transformer moves from the head to the lower cabinet.

I believe Eight Ball Deluxe may have been the first Bally electronic cabinet with the backbox on hinges, yet that design is different from the hinges used on Fathom, originally manufactured just four months later. Also, the neck on Eight Ball Deluxe extends just under the lower surround, and that was changed with following games. Xenon has a swing out backglass door. Another example, Centaur and Medusa, and possibly others, have posts in the middle of the cabinet so that the playfield can be pulled out to rest on those slots instead of wood framing.

Other differences are very obvious: Mr and Mrs Pacman, Eight Ball Deluxe LE, Bally Midway vs Bally. I haven't owned them all so these are just the things I have noticed over the years.

I think you may have mixed up EBD with Medusa, EBD has wood supports and Fathom has the metal support posts in the lower cabinet, plus the neck is different on EBD and uses a different hinge system. Unless of course you just have an odd EBD with some unusual features. I think Centaur and Medusa should work, though. Problem is, EBD and Medusa, Centaur are such in demand games that they would have to be basket cases to part them out for Fathom.

I think you are right about Flash Gordon being first with hinges, it preceded EBD by a couple of months. I don't like the hinges they used on Fathom and such, run into broken welds all the time. You can find the hinges for EBD at your local hardware store, not so for Fathom.

I think Centaur and Medusa are it. Of course, you would have to cover the extra flipper button hole for the demon post on the right side if you used Medusa. Like Hellfire said, plenty of games can be used if you don't mind making some adjustments. You could use Eight Ball Deluxe if you removed some of the wood support rails and replaced them with the metal supports used on Fathom.

Do you need another Fathom cabinet? I have one and you are welcome to it. It is just the wood cabinet, though.

There you have it! Looks like Centaur is it. Probably better off going with new than trying to find an acceptable Centaur cab. Amazing how many small differences there are with these cabinets all made within a short stretch of time.

It has been a number of years ago now, but I remember trying to find a door and hardware for a 1948 Dew Wa Ditty. Ended up buying a parts game and scavenging the door. There were plenty of differences in the cabs from one game to the next back then, too.

I think you will find that the sound boards are completely different. Also, surprisingly little is compatible on the mechanical side. Just off the top of my head--drop target assemblies, drop targets, pop bumpers, lockdown receiver, lockdown bar, backglass locking mech, flippers, spinner switches, sling kickers--most are much different than their Bally counterparts. Even the plastic posts and the hardware used to hold the posts in place are different--not too many t-nuts on classic Stern. Most of the coils are common, though Stern used more variety with their flipper coils than Bally did. Lamp sockets look similar, same lousy performance as Bally. Pick up a few parts playfields to fill in the items that aren't carried by Pinball Resource or other suppliers.