I did the 235 to 327 conversion in a 57 about 5 years ago. I found a 66 1/2 ton in the junkyard that had a complete drivetrain and got everything from the fan to the tailshaft, carb to oil pan for $400. Dropped it in in a day's time. What a huge difference that made. The 235 wouldn't do more than about 55 mph, the 327 would run along at 65-70 and was only turning 32-3400 rpm. 235 was DONE at 2500 rpm. I left the factory 4.10 gears in place.
I did mine on the cheap with what was available to me cheap. Ideally a 350, 383 or 400 would create more torque and about a 3.55 ratio seems to work best with about a 30" tall tire. A 26" tire would be ok with a 3.08 ratio. I understand that rearends are the same width (or close enough) to fit your truck through 72. Those are still pretty common here.
Devin
