My hats off to you sir. I've seen this hitch (ET) over the years (web images and articles) and only now putting name to person as we've now just conversed personally. As I stated I just check the web from time to time as it pertains to the RV hauler industry I once worked in with my grandfather in. I'll admit he was a brilliant man for his time innovating the hitch. As with anything times change and things progress. Trailer weights, larger trucks, etc..... The knowledge I took from my days working with him building hitches and trucks to building off road vehicles incorporating 4 link suspensions systems I saw where your "dual parallelogram" has geometrical benefits.
I can relate to the manufacturing benefits to having an outfit capable of producing a product with precise tolerances. One of the major issues we had during manufacturing was building parts interchangeable from hitch to hitch. When I first started working for my grandfather every part was laid out, cut, drilled and manufactured by hand. I spent the good part of a year making jigs to not only speed up the process but help make the tolerances from part to part tighter. They were still a far cry from a "production line" part, but much better than each individual part being measures, cut, drilled being measured by tape measure and marked with a line or center punch and then cut or drilled to even having templates to cut radiuses with on the bag plates and shock mounts.
I seriously doubt my thoughts of ever bringing the hitch back to life and manufacturing them again will ever come to fruition. I have neither the money nor resources to sink into it to fulfill such an outlandish dream. Had I, the first 2 things I would do would be source it out to someone capable of building it so parts were made true to spec and repeatable and expand upon one of the sayings my grandfather used to use. Build it tough enough to haul a freight train but smooth enough to haul a Model A. Third would be to do such as you and design/build a new head. I saw some major flaws coming with the heads of the day as you stated. I knew back then the trailers were only going to get bigger and heavier so the hitch itself would need to get beefier parts built with different materials and the head as it was was only going to prove sufficient to a short extent. The materials weren't going to prove as a long lasting item. Cast parts just don't seem to have the life of something made from superior steels and proper machining.