I am looking for an experienced point of view on how to go about clearing the oil passages, by someone that has done this, or is familiar with the oil passage routes in this engine design.
Most all of the internal oil passages can't be 'blown out' without removing a part first. And by part, I mean the cam shaft, or the crankshaft, or a con-rod, etc.
As I recall, the head (all the valve train parts) is lubricated from an external wishbone oil feeder pipe that is located under the header pipes. Main line front/center at the bottom. The "T" fitting (welded/brazed) is near the top, and a line splits off to each side of the head.
If you want to check for oil flow to the head, I might suggest loosening the lower banjo bolt slightly and cranking the engine. If you get oil, and *still* think the lines/passages downstream may be plugged, you'll need to remove the cams and rocker shafts.
Not terribly hard, but does take time. Loosen all the cam adjust locknuts and screws, mark the cam chain, the cam gears, crank gear, a tooth on each cam/crank gear so you can get everything back in the same position. Remove the cam chain tensioner, remove the cam gears, remove the cam caps, lift the cam out.
For a warm fuzzy: Remove the two 8mm? 6mm? hex plugs on the right side that are axially inline with the rocker shafts, pull the rocker shafts out, and gather up the rockers and the springs that may (or may not) still be attached to the rockers. I think it best the rockers be re-installed in the same location, so you might want to mark them before removing.
Reverse to reassemble, taking note that the cam shaft caps *have* to go back in the same location, and direction. You have been warned.
Rick