I installed an S-10 T5 in my '48 Sedan several years ago, behind an Olds engine, using a Chevy 10 bolt rear end setup. It fit in the existing X-frame fairly well with only a little trimming. I didn't like the really low 1st gear, as it wound out at only about 20 mph or so, then you had a wide gap to 2nd gear. It was good for getting rolling tho. I loved the overdrive on the road, however, with a 3:36 rear end ratio, road speed was very good, keeping the RPM's down.
The trans wasn't strong enough for the Olds' torque tho, and shelled the 2nd gear pretty soon. At that point, I decided I needed something stronger, so I found a Muncie four-speed and went to work on installing that. I soon found out that room for the side-shift mechanical was nonexistent, so I modified the X-frame extensively. (I don't recommend this approach with the body on the car, for obvious reasons.) It worked out pretty well, but required a longer driveshaft and a little more floor modification for the Hurst shifter. I need to pull it again, tho and check it out, as it jumps out of 4th gear regularly. It doesn't shift as smoothly as the T5 and of course, doesn't have overdrive.
I may have to go back to a Tremec with stronger innards, as I really liked the overdrive. Even with the 3:36 gears and 15 inch tires it seems to need another gear, as RPM's are about 2500 at 60 mph or so.