1968 roadrunner question on rear setup

[70Dustpan]

With the springs moved under the frame rails and the tubs widen to the frame ( mini tubbed ) you can fit 15X12's with 29.5X15.5. This is what is on my buddy's 68 Sat.
As for a good handling frontend on the cheap I would go with larger T-bars, tubular upper control arms, adjustable strut rods, box the lower control arms, and some good shocks.
For brakes there are many kits out there for 4 wheel disc set-ups.