Lee W, Here are some pics of how I've done it. I just copied the way H-D did it. On Frankie, it was easy, as the jugs are already setup for skirt oilers. On the BT 80, I made a template so that I could drill the holes in the mounting flange similarly, and then blocked off the hole to the cyl wall with #10-32 allens. The actual size of the hole through the cyl wall matches the one that H-D used on the K cylinders. Just copycat engineering.
The feed on the 80 is from the sending unit, on Frankie, it comes from a feed line on the BSA oil tank that originally was used for OHV valve gear.
On both, a banjo fitting is held in place with a longer case bolt as the pics show. Also, the right case is drilled larger, 3/8", I believe, up to a point where it will meet the drilling from the cyl mounting flange going down. It all really copies the K design, except that I had to run the oil via the banjo and ext oil line.
Sorry the machines are a little grubby, the closeup lens really shows all the warts!