Are you talking abut going road racing? Developing a vintage Mopar is going to be a real uphill battle. If your only goal is to run Regional Club Races then I'd look at ITE (Improved Touring E). It's a very limited prep class and E is where they place all the cars that don't fit in any of the other Improved Touring classes. American Sedan would be a real tough class. It's a very competitive class that really favors late model pony cars. Engines are limited to 305ci with only a few exceptions for late model limited prep cars. EP (E Production) might be a slightly better fit but again Production is a tough place to compete with an "oddball" car. If it were me wanting to really go Club Racing I'd build a T/A2 Challenger and run it in GT-1 or 2.

That being said what I am doing is building my Aspen as a Pro-Touring car with a NASCAR chassis and an SCCA legal cage. I'm thinking of doing the odd Club Race in it when it's done but absolutely know I would not be competitive given the level of modifications would put it in GT-1 where T/A-1 cars live. The goal would be to have fun and see how many cars I could pass regardless of their class and try to keep from being lapped by other GT-1 entries.

I hate to say this but NASA might be a better place to run a vintage Mopar. American Iron Extreme rules might allow enough leeway for a competitive build.