My recollection is that there was an importer (the name Ameritech sounds right to me) who brought them and somehow got them certified as street-legal in the US. I remember thinking it was funny that the car road-tested by R&T (which belonged to a guy in AZ) had a Jesus fish on it. As I recall they had to sell them with just the front seat for some reason, but that you could legally add the rear seats as an aftermarket item.
If you were truly wealthy, it seems worth going through some hassle to have the greatest roadgoing car ever built.
As I recall, Carmack said he "didn't want" a McLaren, but his F50 dyno-tested far below its rated BHP. He did all kinds of wacky (and stupid IMO) mods to his Ferraris, including turbo kits, and a full carbon-fiber body for his 288 GTO.