Update: Not sure if Dwayne took any additional pics than the ones he sent me after the seat cutting was done, so I'll post what I received FWIW.

Two different views from the intake sides, showing both the "bare" 77919 head and the disassembled 77929 head together. They're not "identical", but there are less big differences in their appearance after the new seats. Dwayne also pointed out some things and recommended measuring same-position chambers on both heads to see how close -- or not -- they are.

This is a 35/45/60/75 seat config. I drove Dwayne (and myself) nutz going back and forth on angles, etc., until settling on this.