You can go with a 3spdOD if you want (same gearing as the 3spd), but the shift from 2nd into 3rd is such a drop that it will be a bit of a dog. That's why the T5 is the better overall choice. A 4spd isn't really much better than the 3spd, as they usually have an even lower (like 2:21 or 2:56) first gear and still no overdrive.
I have a chart at home, but working from memory, a S10 T5 from a 4.3V6 should have the 3.50 first gear, and like all S10's the shifter is in the right spot. One from an Astro van would work also. Get one from '87 or older as it will have a mechanical speedometer.
Just get it all put back together and get the bugs out of it before you get too worried about changing everything. Decide what you like and dislike about the setup you have, then get back to us.
