OK bloke from Vegas here;

These cars are eligible for vintage and modern. For Sports Car Club of America (modern) they rub GTL (Grand Touring Lite) While the A-series engines are run in very competitive national cars most of them have a modern body due to the aero advantage. There are still quite a few 1200 bodied cars out there still. The class itself had struggled for a bit but due some hard working people like Peter Zekert (PJZ) the class has a good turnout. The class allows tube frame cars and is pretty wide open.

As for vintage these don't fit C-Sedan but they do fit classifications for 70's race series rules and most vintage clubs will allow them under the IMSA rules, so you could run the cars there as well. Dave Patten runs his 1200 in both modern and vintage.

Tom