The big question:
Is the wheel track really 4’-8 1/2”?
I’ve heard that is a myth. It is factual that a single gauge was hammered out by the various companies, because after a while they realized they were in the transportation business, and having different equipment just increased labor costs. But there wasn’t a big yardstick laying around from the Roman era. The closest thing to that would probably be the stepping stones on some of the “crosswalks” in Pompeii, which were laid down so pedestrians wouldn’t have to wade through a river of kaka; obviously there was a Roman standard for chariot gauge, or at least a min-max standard of some sort.