I installed a complete front end on my '74 CB750 (forks, wheel, caliper, rotor, master cylinder and fender) from a '80 Yamaha XS650 last year and just recently added the 16" rear wheel from the same model.
The front wheel is a 64 spoke model from the XS650 Heritage Special with a new rim and spokes, which I proudly laced myself! (Three tries and 4 beers). The matching rear wheel is a 48 spoke rim from the same model.
I wanted the better brake on the front from the Yamaha and the look of the 64 spoke rim. The rear idea was to get that newer look of a 16" tire. I had to use a new sprocket on the rear wheel, so I decided to change the front sprocket as well. While I had the covers off, I took them to a shop in Charlotte, NC called "H & H Polishing and they did a fantastic job.