Designed for street 262-400 c.i.d. Chevy V8s that have heads with canted center bolt holes. #2104 is stock replacement/street legal part for 302, 327, 350 V8s with OEM 4-bbl. carb.; except stock equipped EGR. #3706 is stock replacement/street legal part for 305, 350 V8s with OEM 4-bbl. carb.; 1987. Both accept late-model waterneck, air-conditioning, alternator, H.E.I. and have rear water crossovers. #2104 accepts exhaust-heated chokes. For 1987-95 stock aluminum heads use #2101. Will not fit Chevrolet Bowtie or LT1 heads.