With respect to getting a GT40 into SCCA sanctioned racing you might want to look here:
US Sanctioned Club Racing a GT40
But as is it would not pass. It'll be hard to get a GT40 to pass SCCA tech, but I think it possible if one is willing to work within the compromises it will bring to any sort of street use. Once must also consider fuel systems and other things too besides cages for SCCA legality.
Ron