How quickly should oil pressure come up?
its oil flow that counts
i have the joy of 265 6
same pump internals as the 273 318 etc
shifts a lot of oil as flow, never impresses with pressure , does on occasion take a while to show pressure on start, 7 main journals to feed mind.
my sender is electronic the reading on the gauge seems to depend on how much sealer you use, that messes with the earthing :)
if there is some flow you are unlikley to hang up a bearing at idle regardless of what the gauge says. Your starter is punny in comparison to the forces created by combustion.
next time pump is out check cover for scoreing and clearnce between impellor/clover leaf and cover.
if you spot obvious change at rpm when hot say from 60PSI to 30PSI, when 60 is what you have routinely seen...then worry...its very hot or something wrong.
ive been running around for 20 years with oil pressures that hemi 6 people know are fine, but would make 318 people worry. and my journal size and bearing widths are mostly the same as yours
Dave