I've HEARD that there were 10 RHD GT5-S cars made. This is hearsay, as I don't know who told me, or based on what information.
Mine's LHD, and a 5-S, not a 5, so so far we're back to one!!
There was a somewhat active DeTomaso importer in England during the 70's and 80's (actually still exists, although obviously not importing many DeTomasos...) so the number should be quite small but not insignificant.
Being quite serious for a second, I firmly believe that the only way that the world will ever know EXACTLY how many of each model were made, and in what configuration, would be for someone to go through the Factory Documentation serial number by serial number and make a list. I really don't think that there is any other reliable source of those numbers.
I asked Claudia Lodi to do just that for me a few years back. As I mentioned in my last post, I don't quite believe the answer she gave me. She hand-wrote a list of ALL the GT5-S cars ever manufactured by the factory, and it totalled 89 cars. This number seemed quite low to me (if you subtract the serial number of the first GT5-S, mine, from the last "classic" Pantera built in 1990, you get 189 cars. These cars were a mix of various models, primarily GT5-S's I'm sure, so the 89 number seemed quite low.
Prodding further, she admitted that the Amerisport cars were not included because the factory didn't consider them complete cars, and she couldn't tell me how many Amerisport cars were sold. If we figure perhaps 30 or 40, we are still missing some cars in my opinion.
I didn't ask the question of how many were RHD or LHD, but I imagine that would have confused the issue even further!
All this to say that until somebody can go through the records car-by-car, I don't think we'll ever have the answer.