14096217 Iron heads, are centerbolt. They are 1987+ (and later) and feature 72 degree center bolts. Valves are 1.94 and 1.5 with 64cc combustion chambers. 55-86 did not have 72 degree center bolts. These heads were also used on Marine 350 engines, including TBI marine engine. Valve covers for small block Chevy's had perimeter bolts holding them down prior to 1987. Starting in 1987 they went to the center bolt hold down. These are TBI heads made by Chevy and sold to OMC with another casting number to show they are for a boat. Were are your hold down bolts located?