I need some help identifying what is missing. I bought my 72 250 (W114)about a month ago. It's had a M130 (single overhead cam straight six) with a blown head gasket. I tore into the valve job without taking any before pictures. I went to put the thermostat housing back in and there is a hole in the top of the housing cover that something obviously screws into, but I don't know what and nothing in my pile of parts seams to fit. Any ideas?

Thanks

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