Is there a difference between the bellhousings that came off the auto FD transmissions and the one that came with the 20B?

 

AFAIK ALL rotarys use the same bolt pattern, whether it be a 20b or a 13b

 

Right, I understand that part, in addition to the fact that auto bellhousings have the side mount starter and the extra bellhousing bolt, but an auto rear iron will still bolt up to a manual trans and all that. However, I wanted to know if there's any significant differences between the bellhousing from the auto FD transmission and the auto Cosmo transmission? I have been told that there may be a difference in length/depth between the bellhousings (with the 20B version being longer, or something to that effect), or that both can be used interchangeably.

 

not sure, but the Cosmo does use a bigger transmission than the FD, although i think they are related.

 

That isn't strictly true, but pretty much anything '74-newer can be bolted up to any '74-newer MANUAL trans, give or take a few bolt holes.

The automatics get tricky, Mazda moved the starter location and eliminated the vestigial top-mount starter boss that was previously used for torque converter nut access. So you may technically be able to bolt some transmissions to some engines but you won't have a way of connecting the torque converter to the flexplate unless you do some remedial milling to make your own access hole.