E mod is basically a tube frame car/race car. Non-production. SCCA doesn't care if it's a replica or not, only that it is non-production and tube frame. Where we differ on the Spyder from original is fiberglass rather than aluminum but that would probably still run the same class.
I believe that is how Carey and Co. does vintage racing with the 904: tube frame/fiberglass body(as original) and the original 904 had a 4, 6, and 8 in it originally.