Several years ago, a friend had the same problem with his '81 1100. He checked the oil pickup screen - clean. He removed the engine, replaced the oil pump and checked all the bearing clearances, which were all good. He put it all back together, and still had no oil pressure for 5-8 seconds on a cold start. A warm start was better, but still had a slight delay.
It turned out to be a small crack in the front cover, near the bottom of the oil filter mount. It was allowing the oil to slowly drain from the filter housing back into the sump, so during a cold start, the filter and housing had to fill with oil before the pressure would rise.
With your engine cold, remove the filter housing and note how much oil drains out. There should be quite a bit. If not, the oil is returning to the sump - somehow.
I hope this helps, and you don't have to tear down your engine! If you're eventually getting 60 PSI, the oil pump is working, and with no knocking, your bearings - for now - are OK.