my old ride was an '86 5th ave, hot rodded. I rebuilt the front suspension with poly bushings, added a 1 1/8" cop spec front sway bar, monroe sensatrac shocks, 11.75" front brake swap, 5 leaf rear springs, 1" rear sway bar, and an 8 3/4" rear with a 3.55 742 limited slip & willwood 12" disc brakes. I also used some 17x8 mustang bullit wheels with 3/4" bolt on adapters and 255/50R17 tires.

I also ran an A500 OD tranny, and considered swapping an A833OD. my '76 duster has a bench seat with the 4 speed, using that shifter would work great with the stock split bench.

engine, I had a 360 with a comp XE262, headers, and RPM air gap and 600 edelbrock carb to start, but replaced it with the stock roller cam 318 short block, regrinding the roller cam by bullet with their HR259/316 lobe for both intake & exhaust, running home ported magnum heads, and using the same carb & intake. ran as strong as the 360, while delivering 16% better fuel economy (17.5mpg vs. 15 in mixed driving).

stick with the small block, and if you're going OEM heads, stick with magnums.