RB25 AFM I had in my KA with my cold air intake, gets rid of the small restriction from the KA AFM so you can run uniform 3" piping or whatever size your after for the intake.
It works perfectly fine. I had a Z32 AFM on it which is also 80mm but I found my idle was erratic and the car would drive weird on partial throttle, I probably just had to tune the VQ map correctly so it's more suited to a smaller resolution but I never got that far and didn't know much about that sort of thing back then.
So I got the RB25 AFM and it didn't give me any problems!
$150 shipped.