Like any engine combo it all depends on your goals for it. A 451-499 with a 6.760 rod is a stout street-strip engine with a STD port head. My opinion on the 496-512 is the shorter rod requires a max wedge or B1 size intake port. Also 1.6-1.7 rockers and an aggressive intake lobe. Without getting into to much the piston in these combos moves away from TDC FAST and it needs plenty of flow volume available when it does. STD port heads and a larger than needed cam grind can crutch this but the engine will not reach is power potential without enough port AND intake volume. Some calculations on Larry Meax's software is eye opening.