According to these:
http://www.edelbrock.com/automotive/mc/manifolds/chevy/performer-rpm-sb.shtml
http://www.edelbrock.com/automotive/mc/manifolds/chevy/rpm-air-gap-sb.shtml
They are identical in height unless I'm missing something?
Nope you are on the money ( and I crossed my words ). The RPM series whether its an AirGap or not seems to be 4.72" in height
Performer Air-Gap # 2601 or 2604* is 4.32" ( its not part of the RPM lineup and slightly shorter )
* they show the 2604 is for 87+ blocks
http://www.edelbrock.com/automotive/mc/manifolds/reference-dimensions.shtml
^^ this is what a friend is running on his MCSS with stock air cleaner and hood insulation, all black to match his crate motor
Or you can get even lower with or without EGR with the original performer intake 2101 or 3701 series at 4.05"