Does the 3.0 use the same head gasket as the 2.5L car engine? Iboats has the same parts for the 2.5 and 3.0 mercruser head gasket . I had a look online but the pic they have doesnt look the same as my 3.0 gasket.
For critical parts, and head gaskets are certainly in that category IMHO it is best to go with OEM Mercruiser. The cost difference is probably less than a gallon of gas.