Hello , thanks for the responses. It sounds like an aluminum was only used on HIPO engines? And that i need a cast iron housing without the thermostat recess and without the tapped fitting on the top? I have 2 part numbers.. C4OE-8592A or C3OE-8592A. Or should i get a C5OE-8592A? I thought the C5 housing was when they incorporated the recess in the housing and removed the recess from the intake. Any help in locating the proper one would be appreciated. These things are hard to find.. All i can seem to find are the recess in the housing part..