An aftermarket turbo is generally a no-no in the SCCA, except when a specific alternate turbo is allowed (see the Evo specification line in the rule book). This is for the normal "National" classes, most regions have some form of run what you brung class that you can probably run in for fun. Like SPO (super production over), ITO (improved turing over), ITE, or ITX (E/X being extreme).
I think NARRA runs some power to weight GT classes that are closer in spirit to the NASA ST classes.
Of course, this is IF you comply with the safety rules. And as this is road racing with your power you will need to do something to keep the brakes alive and likely some chassis mods.