I run a 270 in my Suburban and have been pretty happy with it. I still plan to pull it out someday and put a V-8 in its place, but its good enough there is no hurry.
To run the T-5 you need a later bellhousing. I don't recall right now if they start in '48 or '49, but the right truck will be a Chevy or GMC with a synchromesh 4-speed or a column shift 3-speed. There are some clutch linkage issues and I'm not the one to try to explain those.
Also they changed how the bellhousing mounts to the crossmember in '54. I suspect you want a '49 to '53 bellhousing, but if you do some searching here you'll find more specifics and hopefully someone will address that detail also. I don't think those bellhousings are hard to find, so make sure you get the right one.
