if it is a truck tall deck 427 then you can take and install a 4.25 stroke bbc crank and stock 454 pistons then run a 6.385 rod i think . hopefully someone will correct me if needed. a friend of mine built one with stock .30 over 454 pistons a 4.25 crank and either stock lenth rods or 6.385 rods and it worked great . it save him lots of cash to not have to buy 496 pistons. makes a nice 500 cube engine