no you dont have to change traz or rear axle

they will take a little HP upgrade

run them till they break then swap to bigger stuff

comp 901-16 springs are good for most cams that are a mild hydro cam,they are a single with damper,drop on with heads on engine,use stock valve seals and retainers

I steped mine up to a small roller cam with the 901s and run the 904 tranz with a high stall loc-up verter