I am still curious whether you installed your own cam bearings or not. The cam bearings have different locations that they have to be installed in and are marked to go in a certain order and have different clearances and can affect oil pressure. One bearing in particular has an oil hole that has to be lined up with a hole in the block, not a groove. I am not saying this is your problem, I just wondered if you did install them because of what you said about being able to see the groove.
As far as your question about accounting for the initial 40 pounds of oil pressure, if the engine had too much clearance and caused a bearing to shift or spin it is logical that it could cause a loss of pressure If that did happen, the pressure is not going to come back. just hope that you shut it down before it did damage to the crank.
The high volumn oil pump that you speak of, is it new? You never want to install a used pump in an engine if at all possible. I would have to awfully sure of a used pump in order to reuse it. I have been through that before. Many moons ago, I tried to save money because of a poor paying job and rebuilt an oil pump with new gears and spring. One of the worst mistakes I could have made. Wound up replacing the crank and all the bearings along with a new pump. Much too costly just to save a few dollars. you either pay now or pay later. Either way you are going to pay. It is all up to you on how you go about it.
Ed