I know the original post in this thread is YEARS old but I've looked at MLC for conversions or multi and here's the general gist.
As has been established in this thread the case splits in two and there are two PCBs. For whatever reason Data East put the CPU on the ROM board so not all games use the same CPU. This means that to do a conversion games must use the same CPU, and it also makes any sort of multi challenging as you'd have to basically put all CPU types on the same PCB.
But it breaks down like this:
Avengers uses a SH7604 CPU
All other games use an ARM CPU
There are some other differences too
Stadium Hero 96 has a DE146 protection chip that no other game uses.
Also most games have scrambled audio data as another form of protection except for Janken Game Acchi Muite Hoi!
That basically means that Hoops/Hoops 96/Dunk Dreams 95 are the only ones the same as Skull Fang.
As Tailsonic demonstrated It's also possible that Stadium hero could work as a conversion donor with the protection chip appropriately disabled.
Also possible Acchi could be used if the skull fang audio data was de-scrambled. This would require more investigation/research though.
Avengers is unfortunately not a donor, nor could it be converted to since it uses a completely different CPU
