4 speed od or 5 speed

Just to point out again, the transmission the OP has and originally asked about and the one I was previously talking about is NOT an AX15.

The R154 is the way to go for that family of transmissions, it came factory in Supra's and has been proven to work with some pretty significant HP/torque ratings even in stock form. And of course there are a ton of aftermarket parts available for them because of the Supra tuner application. Very little tunnel mods (if any) are needed for the R154, and you just have to find the right V8 Dakota bellhousing. I think some custom work is needed to make the input shaft bearing work with the small block crank register, and you need to covert over to a hydraulic clutch.

While this is actually on a Brit sportscar forum, there's actually quite a bit of info in this thread about what's needed to put the R154 behind a SBM.

http://forum.britishv8.org/read.php?6,15981,page=1