oils ain't oils.
When making statements like this you have to remember this is an international forum & what applies to you (regarding oil in this case) may not apply to everyone. I am not criticising, merely pointing out you have to be careful with sweeping statements. In our great red/brown land only those in Melbourne & Tasmania could get away with straight 30w...... in winter.I was thinking of the rocker feed lines but they are in the scavenge side so are virtually open ended. I shall no be so generalised with my comments in future.
Oil pressure could easily be checked with an adaptor screwed into the big end quill or anywhere there is access to the main feed gallery. would need a low reading guage though.
Regarding oil grades , SAE 50 or 20w50 would never be needed with a Vincent , the oil temp is never high enough. 10w40 or monograde 30 are probably ideal.