Engine swap

You don't have to do anything to the firewall on a '63 to fit a small block but it is VERY tight. When I first put a 360/4 speed into my '63 I put a dual circuit master cylinder on but made no other changes. The 7.25 rear lasted about 6 months as a daily driver including the odd burnout (on the original
13" bias plies) until it grenaded then I bolted in a junkyard 8.25. The drums have been swapped out for discs but it still has /6 torsion bars - with the suspension lowered it handles well enough to keep up with other traffic. It will eventually get stiffer torsion bars and a bunch of other stuff but if you're on a budget it can be done bit by bit and still use the car and have fun with it in the meantime.