I think your choices in carbs would be legal with WERA. They are superbike rules and only specify that the carb type has to have been available prior to the cut-off date. The basic principle of the FCR is that it is a flat slide not round or oval. I was racing flat slide carbs in the early 80's. I also don't think anybody in the vintage classes in WERA would protest. AHRMA on the other hand is very specific about flat slide carbs and you probably would get protested.