Kind of surprised of the answers so far but it is 2019!
A good geared 500 is about twice if not triple the gear box! Eventually being geared as a stock 500 config the box will outlast the motor, Even the Kansas boxes,,, Maybe
Why would you want all that big block weight and many times expense vs any junk 350? Or even better a retired LS.
Of course this assuming your going to gear a basic 50 year old motor that has seen 4k maybe once in its lifetime?