Sounds like a good plan, but you will have to get side motor mounts for the 250. The real issue is the crossmember at the bellhousing, which doesn't like the 250/V8 bellhousing. A neat trick I've only read about, was swapping in the crossmember at the bellhousing for one from a 54 pickup. This crossmember will accept the later V8 slanted type motor mount/bellhousing, not straight like your original.
Less work than the T-5 to 235, I don't think so but your thinking regarding the more modern motor is right on. I'm running the T-5 back of a 261 in my 46 and that trans made the truck so much nicer. You may want to go T-5 first then decide on the newer motor.
