While not having actually used a pair of the AMC versions, I have significant experience with E-heads. You "called" the difference between Performer and RPM. With the AMC head, the heat crossover appears to be the only appreciable difference.
Generally, Performer heads are for street use, with port velocity being a more important parameter than port volume. RPM heads are for hgiher levels of power, and some racing.
After reading the stuff about the head (AMC), I feel there are some changes to be made from Edelbrock's original design. "out of the box", low-lift flow is less than desirable. Based on your carb and intake, I believe returning it to the AMC designed 30 deg. intake face/seat would help. The cam you speak of does not need "high lift" flow, as it isn't a high lift cam.
On the "good" side, the head uses studs and traditional rockers. GOT TO BE A GOOD THING! AMC valve train has "issues"... As these are about your only choice for a quality, aftermarket head, you KNOW they're better than any factory head (except MAYBE the old Crane SS heads).
That cam you mention is a little one, you know. As is the Perfrormer intake. Not to cat any apsursions, just to make sure you understand, the engine you describe is a "performance engine", not a "high performance" or "race" engine.
Lastly, most E-heads have lots of "meat" in the ports, making for plenty of expandability. That is, if you decide to step up to serious power, there's room in the heads to port them to MAKE serious power.
Enjoy your Rambler!
Jim