So far the plan is to drill a passage in each head from the rear-most rocker shaft pedestal down to the threaded hole normally used for mounting front accessories, then I can tee off the oil pressure sending port and have external lines to the back of the heads. It'll be a trial-and-error deal most likely, I'll probably need to experiment with restrictors to make sure the right amount of oil gets up there.
Alternatives would be drilling the factory passage down to the cam bearings (sounds like a nightmare) or drilling and tapping somewhere inside the valley (lifter gallery?) for oil feed. I kind of like the idea of having the oil supply on the outside of the engine because it would be easier to detect a leak...?