If they left out the plug that makes oil make a 90 deg turn into the horizontle passage out to the filter and it instead just goes straight up the vertical passage to the main gallery it will still have pressure and actually a bit more since there's no restriction from the filtering material. If they left out the NPT plug that caps the rear of the dr side main gallery horizontle passage you can take out your dist (1st turn the eng slightly by hand to line up the nearest reluctor blade to the magnet to make it easy to get the initial close when restarting/retiming) then w an inspection mirror/penlight see if you can see behind the gallery inside there & see if the plug is missing. EDIT w more thought I would get that cyl on TDC compression & see if there's at least some side to side clearance on that pair of rockers plus pull the bolt and inspect the offending side edge of the holddown as it is a masss produced stamped piece & may have a burr or sharp edge. there are thin round shims (not the ones that go on the saddles to raise the shaft) that slip on the shaft to space the rockers side to side for perfect alignment & one may be called for here to reduce the friction but that'll be dealt w/checked after the psi is restored