73 and later , wide bearing i believe.
Years back I put a 77K in a 72 frame..
After a while I noticed the sprocket shining one side only, and opposite on other end. So I put a straightedge on it and holey #*@+)$. So since that point around 81 , I knew.
My buddy had gotten a nice black F motor, and it was on display... Wanted to maybe use it someday.. When he found out about the shaft being longer, he was upset..I told him it was longer.
He worried about it so much, he ordered a new short shaft, and split the cases and installed it.. The seal say sunken in, but I think it all works. He was not willng to grind seal boss down..