Edelbrock E Street heads are available in a 75 CC version with a more modern chamber design, and are about $1,100. You will have most or all of that in a set of 516's with bigger valves and even bowl port work done by a pro.
The last 383 I did was .030", flat tops with no valve reliefs, .020" in the hole, 516 heads milled .010" with the 1.74" exhaust valve added, (nail head style which reduced chamber volume), and with a Fel-Pro gasket, it was still under 10-1 compression.
I think you would notice a fair difference if you could raise your compression. I would not want to tear into a fresh bottom end either, and a milled set of small chamber heads with a thin gasket is about your only choice.
Good luck, nice car by the way.