You are correct, the RPM is available in both styles, but he was wondering whether to choose the Performer or the Performer RPM. The standard Performer is not available in an Air-Gap version.
I've read a lot on here about the kb167/302 head combo. It sounds like a nice little build with a bit more squeeze and good flow. Just out of curiosity, has anyone run the kb399 domed jobbies with say a small valved 360 or other open chambered head?