I had 516s on a 400 years ago with the Mopar performance 474 purple cam in a charger.
I would actually just run those heads with a cam around that size, something in the 230s duration at .050 and enjoy the car.
Pick up parts for the next build.
Also the 440 source heads will flow enough for what you'll want out of the box.
The only things you should do is gaskets/ port match. I would use the Hughes stainless steel valley pan on any head and scribe that port size on your 516s, port to that size and blend it in
