The casting number 2236494906 is the original ProTopLine Vortec replacement cylinder head. At the end of the ProTopLIne company they offered 2 different Vortec style heads. The part number for the 2nd head is 2236494906HP. The difference being valve sizes (2.02/1.60 instead of 1.94/1.50) and the valve guide is .570 bronze material rather than part of the original casting, to accommodate higher lift camshafts. Also the intake bolt pattern is different to accommodate older style intake manifolds. It also retains the standard Vortec bolt pattern. This head is referred to as a Pro Torker cylinder head. RHS offers both of these cylinder heads as part numbers 12407 (2236494906) and the 12410 (2236494906HP). All of these heads use the same plug measurements. The measurements are .708 reach with a tapered seat and a 5/8 hex. This is a standard size Vortec plug.
Comp Performance Group