Oil coolers

Im building 78 kz 650 and want to install a oil cooler im thinking of removing oil cal bolt and replacing with threaded tube and tapping on a return any one ever done this?

A 750 oil pan will bolt up to your engine and many of those engines came with oil coolers stock. The oil cooler equipped 750's have the take off port drilled and plumbed, or there are other oil pans with a non threaded takeoff which would allow you to drill and thread for whatever fitting you desire.