There is a lot of conflicting information out there on this subject. I picked up a V6 T5 from a 1995 3.8 Mustang and would like to attempt to figure out how to make it work behind the 2.3 in my 93 coupe. Some say adapter plate is required. Some say have the input ground down to .590 and run a bushing. Others say it can't be done. Others say the ratios are all wrong. I've heard everything I can imagine, and would like to hear from anyone who's done it.
I know the input is about 5/8" longer than the 2.3's input is and I know the pilot is larger (.668 vs .590). But, is is possible to have the input reground to .590 and it still work? Perhaps spacer between trans and bellhousing? The engine is really mild, might make 250hp and I'm happy with that.
Using the info you provided, you can cut the input down to 2.3 size no problem. You'll need to shorten the input shaft though because there isn't 5/8" of extra length in the crank to accommodate it. Either way, if it's already being machined down, that's super easy. Even easier if you have a 2.3 input to give them to duplicate. You can't use a spacer without also spacing out the flywheel and all of that is WAY more difficult and expensive than just modifying the input shaft.