Well, it turns out that the dimensions are different on both the shaft length and the head itself. I'm not sure it matters though. The PTG heads are sold with no indication of differences except appropriate cartridges. I think I'll order one of theirs.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.