I would presume that you can powder Coat anything that can conduct a magnetic charge. I don't know why it wouldn't work, but would avoid coating the gasket surfaces. I don't believe it would cause any problems. Not my experience, but what i know about PC'ing. Check with others before using this as gospel.... Good luck.
The other half of your question was about the heads. The 52-53 Merc heads (EAC) on a merc motor produce about the same CR as the 8BA heads on Ford motors 49-51.
The smallest combustion area was produced in the 52-53 Ford heads (EAB) and therefore produce the highest compression ratio available with stock heads when used on either motor.