If someone has installed the 1970/1971 hemi and 440 6 pack 6 quart low profile oil pan you can check the oil pickup to the bottom of oil pan by removing the drain plug and use the stock oil dipstick to see if it will slide under the pickup and pan, if it does sideways, flat and not with it put in the wide way your good.
All the Mopar factory service manuals for those early Hi Po Hemi and Hi Po BB motor recommend installing the oil pickup against the bottom of th eoil pan and as flat as possible
I don't install them against the bottom of the pan but I do use the thin width of the dipstick to make sure it is close and not bottom out flush with the pan
Let us know what you find, you might want to make sure the new high volume oil pump you bought has the black high pressure spring in it and not a stock standard pressure spring in it like some of the new ones have now
If it has the black spring try switching it into current your pump and see if that helps or not
Some racers use to try and run a stock lo po oil pump to gain a little power by reducing the power needed to spin the Hi Po pumps with the high pressure spring in them, NOT ME EVER
I rather use 5W20Wt oil to achieve that result