I bought a comp xr270HR-10 roller cam that s too big for the rods to clear. Unfortunately I don't know the make of the rods I have-reusing a 383 rotating assembly from a rebuilt engine, which worked fine with a flat tappet cam in an old 2-piece block. Was this simply a rookie mistake that can be fixed by ordering a small base circle cam, or do I have to do some measuring? If the later, how do I do that?

Thanks,
Ken