Stripped spark plug threads 75 Dart

If they drilled the old spark plug hole out with the head on, I would recommend pulling the head and removing any chips from the cylinder so they don't mess up the rings...
I am with KK and the OP on removing this head, because there is another reason to put in a new head gasket while there: The original steel shim head gaskets tended to rust out in 2-3 spots on the /6's, where the head gasket blocks some of the coolant flow from going through the wrong casting holes between head and block. So it will restore the proper coolant flow.