I got a reply. He said this:
"Interesting question. I haven't a clue other than manufacturers were always tweaking the design of their machines for different reasons. I imagine they made changes to improve the quality of the machine or to speed up the manufacturing process or to cheapen production costs. I suppose only an insider would really know."

Perhaps this one falls in speed up/cheapen, if KMMs after '48 continued using the other design. In any case, I'm almost done cleaning it up and pictures will follow in a couple days.