Upgrade for '70 Swinger 340 rear

first and foremost the SS springs are gonna put the *** of the car way up in the air. if you're fine with that look, then carry on. but also remember that SS springs are designed as drag race springs and feature more leafs on the one side so the car may sit funny and it will ride terribly on the street.

one of the key components to traction is tire size. so, what are you working with there?

i think a 3.55 is perfectly acceptable street gear. with a "street tire" i don't think you'll get enough bite to hurt a well built 8.75.

personally, i'd build out that 3.55 set, install some HD springs and roll. if you're feeling frisky, cal tracs are always an option. or you could sell all the 8.75 stuff and have dr. diff build out a dana and probably come out even.