FWIW, the 350Z and the 330ci ZHP (ONLY the ZHP, not any other E46 3 series) are in the same SCCA class - B Stock (BS). The cars in a particular class are placed there by a comittee who compares weight, horsepower, aspiration, suspension, etc. and considers the cars roughly equal for racing. Here are the others in the same class :
BS TT (225hp, dual intercoolers) incl. ALMS Coupe
BS BMW 330 with ZHP, all M Coupe and Roadster ('96-'00) M3 (E30)
BS M3 (E36) Z3 6 cyl NOC Z4
BS Chevrolet Camaro SS ('96+) Corvette ('63-'82)
BS Chrysler Prowler
BS Ferrari 308, 328
BS Honda S2000
BS Infiniti G35 Coupe
BS Jaguar S-type R XKE (6- and 12-cyl)
BS Lotus Elan RWD Esprit Europa Twin Cam
BS Europa, Renault engine
BS Maserati Biturbo
BS Mazda RX-7 Turbo ('87-'91) RX-8
BS Mercedes SLK
BS Morgan Plus 8
BS Nissan 300ZX Turbo ('90+) 350Z
BS Plymouth Prowler
BS Pontiac Firebird WS6 ('96+)
BS Porsche 356, Carrera 4 cam 911, Club Sport 911, non-turbo, NOC
BS 914/6 928 (all) 944 (16V)
BS 944 Turbo (all) 968 Boxster
BS Carrera 2, Carrera 4 (964 chassis)
BS TVR 8 cyl and V6
BS Toyota MR-2 Turbo