I've run across some threads on this and other forums suggesting the very inexpensive and compact oil cooler adaptor from the DOHC model could be used on our CB500-550-650-750s.
I found that the adaptor plate, while using the same o-ring and 20mm diameter oil filter bolt, will not physically fit without some machining, and rotating it 180 degrees so the inlet/outlet ports point down 45 degrees. It can be done, but a wormhole maybe best not pursued.
Any source for inexpensive oil filter adaptors?