As you know 25 ain't gonna cut it. I dont have any mag experience but I cant see the lifter feed hole height being a problem at least as far as system PSI as long as there's no leak from the horizontle gallery cutouts past the lifter body OD unless I'm missing something especially with the poster above who swapped over and no problem. I'm assuming all gallery pipe plugs are there. I would confirm with another mech gauge at the top rear of the block & likely pull/check the pump relief valve/pickup for cracks but I'd eliminate everything else before I took the pan off again. I'd pull the intake & prime it & see what the lifters show for flow and if you could block the filter then see what you show for psi which would confirm the gauge (& the pump/pickup) by eliminating every potential downstream leak. The mini freeze plug that gets driven in the block from under the #5 main cap could only restrict flow if it was in the exact (improper) position partly blocking either of the 2 horizontle galleries out to the filter boss rather than being driven up to it's correct vertical height position inbetween the 2 galleries. Not likely but I'm just tossing stuff out. Holler with any news. EDIT the filter nipple is 3/4-16 so you could get a female cap to block it off there