Was curious about the ' 5MC ' ink stamp on the reproduction regulator. Seemed to be a FORD date format ?
Here's some pictures of a NOS C2DF-10505-A regulator for a 64 6 cylinder Mustang with a generator (I opened the box myself) with the date code on the bottom.
Note the indented terminal identification on the cover in the first picture.
A date code of "5MC" (the "C" may be a "6" - or not) is not correct. 5M6 would be better, but there are other problems.
Jim