A few comments based on building a 496. The 512 will like to breath; any porting you can do on the heads to increase flow will really help. With a cam like the .557 I think you would be fine up to 10.4 - 10.5. Maybe a bit more but personally I'd build for 10.2-10.3 to have a little margin.

On the cam, it depends on what you want and like. The .557 would work great on a street strip car. It would be fun to drive with lots of torque. You would give up some on the top end vs a more radical cam... but the more radical cam may reduce the fun of driving it. The 557 should work fine with standard Ed springs.

With the 557, torque should start building pretty fast starting below 2500 RPM. 4200 stall may be a bit much. I'm not an auto guy but would guess 3500-3800 would be more than enough.