Whoa! Long post. Will try to answer. Ok, breeching dees I can get from Aaron martin or Abbey England. Or forge myself. Not sure which route to go. I'd like to have a separate dee on the topside of the big dee for the hipstrap. Like a two strap halter ring. That would be awesome. I'm not really sure how you put the layers and ramps, could you provide a photo or drawing please? Ok, 4" was a bit reactionary, it's just that the local ones maxes out at about 1 1/8". Let's say 3". So you have the base, and then layer folds over to hold the D-ring? How well do you fasten the side strap billets? Or do you have smaller dees for them?
Also while I have you on the thread, how do you make your traces? I'm not sure I can get all the length for one trace from a hide. Should I cut traces as long as possible and then use chain for the rest of the length or is it even remotely possible to piece them together? Is it only one single ply of leather in a trace? What's the breaking limit of that? I until now only used tarrep hemp ropes (1" diameter) that attaches to the pull rings in the short traces from the wooden hames. (see attached photos of typical Scandinavian harness and rope traces). But it's clumsy, and I now need longer ones as the traces attaches directly to the hames. And I can't figure out a way to attach the ropes to the trace attachment thingy.