there's no surefire way to tell just by glancing at it, honestly, they look very much the same... casting numbers on the block or by pulling a valve cover and checking the head casting numbers could tell... 350s and 305s TPI had different sized harmonic balancers stock, but chevy guys, like us, modify their motors, so the size of the balancer isn't a good way to tell either
you'll probably have to take his word for it, or just run him and shut him up
