What do you think of proposed 505/512 build?

Yes that should work. We just finished up an engine like that for a hot street/strip car and it made 710 hp on the dyno. It was a 508 with Molnar crank and rods, Diamond pistons, 10:1 compression, Comp street roller cam, TF 270 heads and a ported 440-2 intake. We used a Holley Sniper fuel injection kit. Made 710 hp on pump gas with 2 inch headers. It does take some money to put these engines together. I think the total bill was around $15,000 for the 508. The parts are expensive and there is a lot of labor for the precision machining and assembly. When you're making 700 hp in a stock block everything has to be just right or else it won't stay together.