I think note #3 is particularly pertinent:
"Thirdly, some Norton's can have an anti-drain valve fitted inside the timing cover, (AFTER the oil pump), this prevents the seeping of oil down onto the bottom of the crankcases. On Dominators & Commandos Pre 131257, a modification can be made to your timing cover, if you send it to us, (see workshop services code WB12). On Commandos with engine number 131257 onward, a new timing cover, (066161A), can be fitted to solve the problem - see picture below. ** PLEASE NOTE ** This is NOT the dangerous type of anti-drain valve, which is fitted by some people into the oil feed line above the crankcases. Anti-drain valves fitted into oil feeds, always cause oil starvation to the big ends for a brief time when starting the bike. If you use a tap instead and forget to turn it on, it will totally blow up your engine. "
I've tried the inline feed check valve. ZERO hot oil pressure at idle. This is with a new pump. Threw that sucker underneath the bench.