K1 rods or 198 rods, dome pistons, bore the block a pretty good size, ported head, milled head, 4bbl intake, 4bbl electric fuel injection
then a nice forged cam. and crank, push rods, etc... decent exhaust and maybe some spray. 500 hp out of the motor is not the same as 500 hp out of the car.
you would need to build a 904 with specific gears and a decent rear end. maybe 8 1/4 or the usual 8 3/4.
thing is, no one does after market heads so your looking at 2k in head work alone, about 3500+ to build the motor.