"Alleggerita" says that RHD GTA's started at 752 5XX, so 507 is indeed a super early GTA, indicative of an A/D car. Incredible American racing history!
My car was not A/D, but Paolo Franchi, the original owner, was the son of an Alfa Romeo dealership owner in Siena, and lucky young Paolo got a new car to race every 18 months or so. He said they put every A/D part they could on my car back in the day. Of course those parts are long gone.
Like most racing GTA's, my car apparently went through several body changes, even becoming a 'silhouette' car at one point, says Paolo. Nothing more useless than an obsolete race car, right?
Remember, the GTA Jr's did have the high rear wheelwells, which allowed a wider wheel to fit. GTA's had the low slung rear wheelwells like early Sprint GT's, necessitating those cool 'codolini' blisters.
Steve Schaeffer
AR 613 169