Actually, I have it on good authority that the 512S was designed for use on road circuits and tested extensively in the countryside around Maranello. Regardless, I have been having a blast racing those 1970s midship prototypes in Horizon, so I am inclined to disagree with the sentiment that they do not fit the game.
Also, both cars were added after T10 ceased support for FM7, so it doesn't really make much sense to say they should have included them in that game's roster. Of course, I will be the first up in arm against Xbox Studios if they will not be a part of the next Motorsport without any good explaination; I am still incensed at the departure of the Nissan Safari Turbo, and other cars, like the Alfa 8C and BMW 328, that would have been more at home in Horizon's streets than they were in Motorsport's circuits.