Please excuse me for going OT. But you have inspired me to wet sand my hood and try to find numbers. As I mentioned (Years ago ), I am convinced that my truck is an M-724 that has an M-715 bed on it. There are just too many clues to that fact. However... the data plate was missing. And, there is no VIN stamped on the right front frame rail. There is a fifth wheel setup welded on the frame over the rear differential hump so I can't check there... yet.
My truck is titled as a 1969 and it has the original carburetor mounted air filter without a governor. That would be consistent with an M-724.
Ya got me thinking. If I find a number which is consistent with a 1969 number, it would make sense and tie all things together.