just wondering if the tranny out of an 88 GXL would bolt onto the 12a in an 85 my friend has.

 

Yep.


You need to swap the shifter housing/shift rod to make the shifter line up, and the tail housing so the mount is the same, but yes it'll work. The N/A tranny pretty much stayed the same since '79 except for improvements here and there, and it's still in use in the Miata.

edit: I hsould point out that the 5th gear on an FC is way tall compard to the 12A trans. I find 5th gear on my '85 is too tall as it is and I usually use 4th. The FC 5th gear might be totally unusable if the car has stock rearend gearing. The 12A doesn't do much below 4000 rpm...