Hi Lee
It's my understanding that within the various iterations of GT40 about thirty Mk1s were built as "road cars" to be sold to the public as part of the GT homologation requirements in order to race the car in the "GT" class. These road cars were all RHD, more trimmed out than the race cars and slightly detuned.
Some of these cars. in private hands, were upgraded to full race specifications.
The MkIII was built to what we know think of as a "globally federalized" specs. These GT40s had unique many features including flat floors, bumpers, raised headlights, extended rear clip, rerouted coolant pipes to the sills rather than central tunnel and some were built as left hand drive cars.
Cheers
Ian