Which block? RB is not the best idea because of mains, B will wear out quick because of short pistons. Oil system needs to have external pickup(s). Heads are WAY too small. Start with max wedge ports, and a cam at least 20% larger than the .509. I would be looking at something in the .650 lift and 290-300°@.050 cam. The intake is as good as the long rams. It will peak very low, and loose power after that. Think large.. VERY large runners and plenum, and at least twin 950HPs. The 727 will need to deal with much more than 500hp. The torque will be brutal. A nice street combo is an RB 512, with cleaned up RPM heads or a better choice would be RPMS with one of Modern Cyl Head's programs and a cam in the 270°@.050 range with a big carb or tunnel ram. The pistons are taller, the stroke is only slightly more (4.25), the oil system can be inside the block, and it will last. It will also give you close to 600hp and 600 torque on pump (91) fuel, or higher with porting. Bigger is not always better. You build a snotty big engine, or you can build a monster big wheezer.