I just pulled a 250 out of a 49 GMC 100 (1/2 ton). It needed more work than I wanted to put in it.
The 228 that came in the GMC was longer than the Chevy 216/235/261 engines and based on what I observed with the 250, it is longer than the 228. The radiator on the GMC is already mounted more forward than the Chevy. There would have just barely been enough room for a mechanical fan but it sat too low so an electric fan is required. You may have to relocate the radiator alittle more forward, if so thats doable.
You'll need to cut the toe board and bend or cut the center panel for tranny clearance.
The 250's lower belt pulley barely cleared the GMC's front crossmember, I'm talking approx 1/4" - 5/8". Too tight to be able to get an alt belt on the inner groove without lifting the engine a hair or 2. So make sure you get a 3 groove lower pulley.
The 250 was bolted to a TH350 trans
Heres some pics: right side mountleft side mountbalance barely clears the front cross memberright side view in engine bayleft side view in engine bay
This pic shows how the toeboard was cut and gives a pretty good view of the lower clamshell motor mounts:Pic
Theres a bit of work to installing anything other than an AD era engine in an AD but a 250 would be alot less work than a SBC.