Oh, cool, good work LX5 :3
SA-1 didn't move $7F837D, so you don't have to remap it... But on other side, SA-1 can't access it so if you know the SA-1 chip will run on this code (in doubt, test if the stack pointer high byte is $37, if it is, make the game crash, so the game will crash if it's running SA-1) If it's SA-1, you will have to around the code that modifies $7F837D+ and do a SA-1 -> SNES IRQ)
Note that I made a SA-1 version of the Fade in Pack (I mean, made the code get processed by SA-1 instead of simple compatibility workaround), at least the circle one, that has zero lag. It's on C3, but I may need to update it since I detected a small issue with SA-1 version that happens only on Snes9X
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