To answer your question about the GH - it does not have dome tabs. Also, the original helmet had a 1" spacer in the dome, where the tabs were attached and plugged into the tabs on the face-mask. Not a very good mounting system, which is why it was improved upon in the following films, with actual mounting rings.
Basically... you can make whatever type of mounting system you like to make the dome sit securely on the face mask and not budge. Some use the original dome mounting systems, while others re-do them completely - check out the Celtic Touch and BAT helmet for complete re-works of those... I'll see if I can find some pictures and post here.
In a recent thread on the RPF, someone had used a skater helmet, iirc, and fixed that on top of the face-mask - which would also support the dome at the back, so it don't get pulled back and strain the face and dome system. I plan to do something remotely similar to my JediJeffrey face, when I'm going to add a dome mount system, as I want it to be able to support the lot heavier DP DLX copy dome I have without straining and ultimately breaking the face.
Though... I'd have to say that the Celtic Touch is the most ingenious way of redoing the mounting system I have ever seen and it is one of my all-time favorite helmets.
With the adding of small rubber bracer's on the brow, sides and the back, you have all-round support of the dome, as it rests on the face and perfect angle and position every time.
The surface of the kit looks decent enough, but I still think the insides was enough for me to run screaming for the door, when seeing it. Oh man... that was really bad looking - a nightmare, imo. Seems you got it worked out though!
Good luck