1969-1976 cb750 k tanks will interchange as far as the frame mounts go, the 1975 and later cb750 f tanks are longer and would require some mods to make them work. the only real difference between the years of the cb750k tanks are the location of the petcock. 1974 and earlier have the petcock on the right side, 1975 and later they moved to the left. same deal as the tank, 1969-1976 seat pans are identical except for a few minor differences, 1977 and later 750k bikes and ALL of the cb750f series are different. the 750f frames have different rake and trail specs and theyre also longer and heavier. none of the body parts (tanks, seats, side covers will interchange between the cb750f and cb750k. the 18" front wheel, that i do not know, why did you want to change over to the 18" wheel? with the cb750 speedometer drive the way it is, unless you run a tire the same exact diameter as the one on the 19" wheel the speedo readings will be off, assuming youre using the stock mechanical speedo drive mounted on the front wheel. the front ends will swap out between the 750f and 750k series bikes, my 1974 cb750k has the triple trees and sliders from a 1975 750f on it, the top triples are different from the f and k bikes as well, the gauge mounts and the fact that on the 750f the ignition switch is mounted up there as well, the stock 750k swtiches (from 1969-1976 anyways) mount on the frame on the left side right at the front lower corner of the tank.
