Candor1,
I have a CB750 K6 that I bought brand new in 1976. I put a Lockhart Oil Cooler on it when I bought it on the advice of the shop. It does work. That's the good news. The bad news is that Lockhart no longer makes them and you'll have to look and search for one. From doing some searching myself, The hard part to come by seems to be the Adapter Plate that goes between the Oil Filter and the engine. If you can find that, you could use almost any Lockhart Oil Cooler radiator. The HA500 radiator is what I have and is easy to mount on the frame. Wish I had better news for you.
Charlie