For a winter project I want to put some 21" spoke wheels on my 77' CB750F. Right now I have the stock mags on there. Originally I was going to find a 77 or 78 CB750K, take the rim hubs off them and lace them to the 21" rim. The only problem is that the rear of a K model is a drum brake, not a disc brake like the F model. Then I thought to use 2 front rim hubs and do it that way, but then I realized there was no place for a sprocket. Is there anyway around this? Are there any of methods of putting on 21's? Are there other models of CBs or honda hubs I should start looking for?