Go Here. http://www.montgomeryvillecc.com/fiche_section_detail.asp?section=125286&category=MOTORCYCLES&make=HONDA&year=1978&fveh=2986

The blowout diagram gives all the gears a reference number. Go to the table below it, find that number, and at the end of its part name is "(numberT)", indicating how many teeth are on it. That link is for the 78F. Just click on cb750F right above the blowout diagram to switch to a K model, click on the year to change the year... good luck! you can match part numbers as well, to find out what parts are interchangable between the two.

The gears could be popping out because the dogs are worn out. Dogs are the round nubs on the side of the gears. If youre hard on your tranny, they get rounded, and dont hold together well under acceleration, and will pop out of gear.
joe