Is this a stock unbushed lifter bore block?
If so all the stock blocks I've prime with the lifter valley cover off, regardless of which type lifters in them, leak a lot of oil around every lifter out the top and bottom.
I've had similar issues with solid roller lifters that leak a lot MORE oil out at max lift that affected the oil pressure, that block was an early 1966 Street Hemi block that the driver side lifters leak some at max lift and the passenger side galley didn't
I plugged the left lifter oil galley off with a small welch plug behind the oil galley plug to fix it and later had to add another plug behind it when the oil pressure and maybe motor heat allowed it to move forward and start leaking a little more. That motor held 75 Lb. oil pressure running but t would pulse the oil pressure at idle around 5.0 lbs. between 80 and 75 lbs.: work:
Murphy love US