I think the myriad of options and hence grouping of regulations, makes a two-class system viable. Series standings would be according to the classes.
Since we are only counting lowest ET per 40-lap heats, that simplifies the Points counting.
Since we are also doing single car heats, there is not an issue of competing directly against a different class.
To start the series, we have the Concours, and points assigned (These could be held in secret by Marc/SM until the series end). However, this would prevent late (mid) entry of cars (for the Concours), assuming the Concours would require all cars present so they can be ranked.
Then, per round, a car is registered in the class (which cannot change) and points are allocated according to Place within the class.
"... get on your bad motor scooter and ride!"
Sammy with Montrose