Thanks. Just ordered one. The seller jtmarks77 (on eBay, but somehow related to the forum) said it would fit other K years in his description too:
-1969-1971 CB750 K0, K1
-Will also work on 72-76 CB750K if you don't have the full grab rail on
-If you are trying to get it to fit on other bikes the holes are 7 inches or 177.8mm center to center