I've been doing research for a while on this T5 now, and just when I think I have a plan, things take a turn. There are a couple of 5 speeds for sale near me that could work for my application... 1989 S10 w/2.8, which I could do the Jeep input shaft conversion and wa-la. But there is also a 1991 s10 w/4.3 5 spd that's for sale. Now I know that the rear of a 4.3 is the same as a small block, so one would think that the transmission would bolt right up to my 250, but I can't seem to get a comfirmed answer as to whether the 5 speed behind the 4.3 is either a T5 or an NV3500. If it's a T5, then wouldn't that be almost perfect like the hard-to-find Astro T5? Or is the tranny really an NV3500 and I should steer clear?
So, what tranny comes in an s10 with a 4.3 V6 (1988-1992)?
As always, thanks guys.
I am a self proclaimed T5 addict.
I agree with Mitch, that S10 will have a T5. You will still need to modify the input shaft, even though it is from a 4.3 V6 truck. Ask the owner if the transmission has an integrated bell housing. If it does, then it's NOT a T5. All T5 transmissions bolt to the bell with 4 bolts. A T5 will never have an integrated bell housing.
Both of those T5s will be non-world class and have a pulse style speedo sender, NOT a cable connection.
Both S10 T5s would be ideal candidates for a Jeep input shaft swap.
As a general rule, the 4.3 V6 should have a OD gear of 0.72 and that is a good match for a 3.73 rear. The 4 cylinder S10s usually have a 0.86 OD gear which is a good match for a 3.42 or 3.08 rear.
My website shows how to calculate the 5th gear ratio before you buy so you know what you are getting.
I have several T5s on hand just in case you find yourself in my area, but I do ship. 
