Production GCR authorized modifications D.4.a.1 still reads 4 speed + OD = 4 speed unless the cars spec line allows it....Other categories may be different... Not that I wouldn't mind trying a 5spd....but I don't have an exemption on my spec line like the EP class triumphs do..... Thanks -S Scott Cypher SCCA # 362573 #57 HP Spitfire 1500