I’ve built both a VW and a Ford based CMC (FiberFab) TD kit. and they bodies are TOTALLY DIFFERENT. The amount of work involved doing what you describe is not worth the effort (my opinion).
First, the bodies are not even the same size. The VW TD body is smaller and the fenders are different (narrower). Their wheelbases are not the same, the Ford body, being slightly longer as well as wider. There is really not much in common other than the TD styling shape, the doors and grille. The bonnet and boots are not even the same.
If you don’t want to build it as a VW based TD why not sell it to someone who does…put the cash towards finding a Ford based TD or whatever.
The car you describe building is out there. It just doesn’t have the TD Body. These kits are much more economical to build too. Most of them are based on the design of the Caterham or Lotus 7.
Next weekend is the Carlisle (PA) Import-Kit/Replica Nationals. These “pocket rocket” manufacturers will be there. You can also get more info from the Kit Car Magazines. Who knows, maybe there will be a used or unfinished project Ford based TD kit there too?