Imho
Ron -
To include the vintage racing aspect, my suggestion would be to go to Lee Holman. He has the original dies and molds, and will remake a GT40 - although it may be a bit pricier than a Superformance, CAV, or ERA replica.
I would order it from him in a Mark II configuration for a small block Ford, less engine, but with a Kar Kraft transaxle, and the original design "Bundle of Snakes" header/exhaust system, along with an additional collector/exhaust section which includes small mufflers for road travel; include the oil and transaxle coolers, and period correct braking system, but add a current fire suppression system to the package. Consider leaving a location for an oil tank, in case you want to go with a dry sump.
I think the Mark II configuration will give better brake and engine cooling, as it was designed to handle either the small or big block (427) engine.
I would order it in right-hand drive, and without any extras such as air conditioning, radio or other foo-foos.
I would then procure either a Ford small block 289 or 302 block, and have it built up with GT40 racing heads (available from Ford Racing), quadruple Weber downdraft manifold and carburetors, forged pistons and the appropriate rods, crank, and ignition system. Build it in either a dry (preferred) or wet sump configuration. You might also consider the big block version, which will fit into the Mark II configuration, although either could be changed out easily later. The big blocks were wet sump engines with large pans and a single or double Holley carburetor and intake manifold. Use an engine builder you trust who is near you.
I don't think Lee can get the Halibrand knockoffs, but I believe there is a BRM equivalent wheel in the period correct size. Get either Goodyear Eagle, Firestone, or Avon tires in the correct vintage size.
Just my take -
Ralphie