Ranger,
A GTD 40 is one manufactured by a company called GT Developments. They were based in Manchester, then Poole and now somewhere in the midlands of England. The rights to construct the car I believe was sold to a South African company (CAV will confirms this I hope) but I have heard that GTD still are allowed to support their racing cars.
The cars were the second GT40 to be replicated, KVA being the first and the person behind the company was Ray Christopher who is a good guy. I believe he has retired ( we never retire !!!!).
I hope this helps.
Robert