Can't resist the temptation to chuck in my 2 penneth!
Rather than jigging a 'new' GTD chassis, A much imroved end prduct could be achieved by jigging a GTD chassis that has been modified to incorpirate siting the engine & 'box lower on the chassis, plus maybe rear suspension pick ups better placed for improved geo.
At a bare chassis stage modifications could also allow for a bit more room in the footwell, etc etc. Lots of GTD owners have done these type of mods.
With regard to the rest of the car, I believe very little was actaully made 'in-house' by GTD. I'm sure many of the companies that actually produced the parts are still around & if GTD no longer exisits they could manufacture & sell the parts direct to owners without worrying about breaking any contracts or agreements.