What and where to clean up Edelbrock RPM's?

That's doing it the hard way.

I can make one left turn or make three right turns to get going the same direction. Similar situation here. Lots of extra work and cost IMO to use a poor chamber to start with.

Even with positive deck piston, I NEVER use those open chamber heads. In fact, every set I've ever possessed, the entire chamber gets milled off.

Lots of ways to skin a cat.