Don't you have a loop above the entrance on the top line already? If so then that line should have some oil sitting between the fitting on the pump and the top of the loop, correct
I would install the anti drain back valve as close to the pickup as I could get it so it traps oil between it and the pump
I haven't had any troubles with the dual line Milidon oil systems not making oil pressure after sitting in a long time(5+ motors)