If the GT40 were allowed in SCCA it'd be in a SP class, and that would require a GT40 that is prepped to a level that I have not witnessed on this forum or heard about. In fact, I've not looked at SP requirements but seeing cars that run there (ex-NASCAR, ex-enduracnce racers, ex-road racers) it'd be a serious undertaking. I'm sure it could be done, but it'd take a lot.
NASA has treated replicas better than the SCCA with the creation of KC1 through KC5 classes, where (correct me if I'm wrong) KC1 is under 100 rwhp, KC2 is under 200 rwhp, etc. and I think KC5 is 500 and greater rwhp. But, like many NASA events there are so many damn classes it is like everyone wins since entrants are spread out. There is the Honda Challenge, with subclasses no less, and you could end up being first in a class of one. KC classes in the SE are hardly, if at all, populated. But, I think NASA is the best bet since they at least realize replica/kit cars and will allow them to run with proper class equipment.
I've sort of figured I'd use mine in track and test days, while using the race cars for real racing. I'm 100% sure a SCCA competitive GT40, if we could run it in SP, would not be anything you'd want near a street.
Ron