Hellfish:
I'm a new guy here, and just getting back to my 'roots' of older Chevies. I will not claim to have anywhere near the technical knowledge I've seen in the 2 weeks I've been reading the posts I see, but I will offer you my experiences.
I was able to completly trash 2nd gear on a torque-tube transmission with a STOCK 216 back in '61, so if you intend to drive it hard, beware. I think (but not 100% sure) that the '48 trans is the same as the '54 as far as design and dimensions. If you want to keep the column shift 3 speed, but want a heavier transmission, I would think your best bet would be to go with a '55 or later 3 speed with an open driveshaft. I'd think an all Chevy set-up from trans to rear ('55-57) would be the easiest.
I'm presently running a 216/torque tube, but am going to convert to a 235/open driveshaft with a Saginaw 4 speed and '55 Chev rear later on this year. These parts were fairly cheap and easy to find.
