We offer a GP single and a GP-T Twin in Mason Dixon. This class is now my second biggest class (or just as big as GP) with extremely fast laps times. Yes, despite what others say, The twin is faster,( I run both) you can click up and extra gear and it will pull you out of the turns faster. We allow up to 44 cubic inch. You can get these engines very cheap. Florida and Michigan are running these too with much success. If you go BP, your investment will be in the thousands...unless you buy a used BP from a reputable racer.
Note, USLRMA and ARMA does not recognize GP-T