Your stock torque converter will limit your cam choices more than your valvetrain will. I have 20+ years on a 292,.501 Comp cam with stock rockers ,stock pushrods and stock valves in a street car. Only one rocker failure in that time. Bent two pushrods once when i had some overkill MP valve springs on( can't remember the part # but they were the springs that the 590 solid calls for). I wouldn't go more than about 230 duration at .050 with your stock converter. The big Summit cam might be a good choice for a low cost cam.