for those that are interested these are the chips used
for the most part you'll need 7x m27c0801 4MB EPROMS, 100ms or faster
u54, u63: revision ROMS, U2-U5: sound ROMS
and you'll need 16x or 20x (depending on the game) m27c4001 8MB EPROMS, 100ms or faster
u110-u33: graphics ROMS
There is also a PIC16C57 security chip (u64), though I don't know how that factors into these conversions.
as for which games use which EPROMS:
16x graphics roms:
2on2 open Ice Challenge: u118-u133
Rampage World Tour: u118-u133
WWF Wrestlemania: u118-u133
20x graphics roms:
Mortal Kombat 3: u114-u133
NBA Hangtime: u110-u113, u118-u133
NBA Maximum Hangtime:u110-u113, u118-u133
Ultimate Mortal Kombat 3: u110-u113, u118-u133
I pieced this together from posts on KLOV and looking through MAME source:
https://github.com/mamedev/mame/blob/master/src/mame/drivers/midwunit.cpp
According to KLOV there are some PCB differences between the 16chip (4-row) and 20chip (5-row) games. the 16 chip games have some extra timing hardware:
https://forums.arcade-museum.com/showpost.php?p=2985878&postcount=21
According to that you can convert a 16 chip PCB to a 20chip game, but you can't convert a 20 chip pcb to a 16chip game. so MK and NBA games can only be converted to other MK and NBA games, but the other games can be converted to any other.
The components are an ST MK41T56 and a small crystal; I don't know if a 20chip pcb can be made to work with 16chip game by adding these parts.
Please let me know if I got any details wrong.