If there is NO oil getting to that side after running it, and other side gets plenty of oil, I believe the 4th cam bearing was installed incorrectly. I would probably resort to some trickery that would involve a long 1/8" drill bit and strategic lineup of cam before a little drilling is done. This is provided that the path to cam is a straight shot after removal of rocker shaft, which I think it is. The trick is to line cam up first, then drill hole in bearing, then immediately prime oil system and catch the filings coming out the top, with rags etc, before re-install of shaft. That's just my thoughts on correcting somebody's mistake. It could have a ball of casting crud stuck in there too. SCRATCH that. Just checked a 906 head, not straight shot, angle at top of head rocker pedestal, straight long bit won't do it.