David,
By the looks of the bolt hole spacing it looks pretty big to me. Maybe it was built from plans?
(No one in my neighborhood could afford an MK kit back in the 70's and they were hard to find. Airline pilots and doctors had them as I recall. And we lived in a pretty affluent area. I think Tommy Tiger (TWA L-1011 Captain) and Richard Verano had them in SoCal, maybe Dave Wilson (pros). I mostly remember Tiporares and UFO's. I think the proliferation of them is overstated today in regard to the general flying group back then, pros only maybe. Just my thoughts, I could be out my butt.)
Chris...