I have used a pushrod in the lifters with them fully submerge in oil and pump them(the pushrods in the lifter cups) up and down until all the air stop coming out of the sides of the lifters to make sure they where full of oil and not the factory anti rust stuff that is in them scope
I have also soaked them like your doing and then used a drill motor to spin the oil pump over to prime the motor and then used the starter to spin the motor over with no spark plugs in the motor 20 to 40 RPM several times to fully lube the rocker shafts and rocker arms thumbs

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)