There is a forum over at 4x4wire devoted to Isuzu diesels that might have some useful info for ya. Go to:
http://www.4x4wire.com/forums/postlist. ... oard=UBB74
Be sure to scroll to the bottom and set it to display posts active from all dates. I think the default is 2 weeks, and there is a lot of posts going back a long ways before that. They are more aimed at Isuzu rigs, but I'm sure they'd be more than happy to discuss motor topics on S10/S15s. Heck, if there are some other options for interchange of parts besides just Isuzus they might be thrilled to hear from ya.
On the trans, I don't know for sure, but perhaps Isuzu beefed up the trans some when they went to the C223 Turbo diesel motor. I know the C223 and C223T motors are basically the same except the turbo was added, so the newer trans should bolt up to the motor. Drivelines and clutch parts may be different though.