The big block 600 has a line on each end of the crank that lubricates the outer crank bearing. If you go to pre-mix, those lines won't be putting any oil to that bearing. It will still get some from the premix, but not near as much as the direct line.
When you premix, you mix at one ratio, probably 50:1. That ratio is very rich at idle. The oil pump will change the ratio from maybe 150:1 at idle to as much as 32:1 at wide open throttle, so your oil consumption is greater when there's higher demand.
I'd keep the pump.
2007 RMK 700, 2008 RMK 600, 1995 AC Prowler 2-up, 1980? AC Cheetah