Mark, do you have a Mk3 available to build the frame jig and 'glass moulds from? What welding process do you intend to use, TIG, brazing or MIG ? Are the frames to be nickel plated?
Flowerpot Ben has mentioned Adrian Moss and Gerry Lisi, the guys already making Metisse replicas. Have you checked if either or both of them might have some kind of copyright on the design?
I totally understand that you've probably dismissed me as a doubting 'asshat' because of my cynical take on your idea but I'm honestly interested in seeing this come to a fruition. One of my true passions is to make the pre'65 class accessible to everyone, not just the leather patch elitists who seem to want to block any innovative thinking on increasing the classes support. If your concept can bring more people to what should be the sports showpiece class, you have my support.