Cam swap cause Oil pressure change?

Fix the leak 1st, that's where you start.

My exp w/relief valve issue were always stuck at a lower psi, typically.
Like no more than 20 psi no matter rpm.
One time I just said fk it.. rev'd it up to 6500 at idle.... and bam, the psi jumped to normal again
Junk in the relief valve.
That motor in particular say on a stand in a bag under a tree for a year.. never run rebuilt short block 318, steel crank, big rods, cheap .020 pistons. Back up motor.
I took it apart, sanded some pits from moisture on journals, flipped the pistons direction for torque...through all the same bearings back in some used heads, new 340 cam n lifters and buzzed it 5800 rpm in front of a 4 spd. Still runs, parked it for the .410