A lot of lifter suppliers are recommending not soaking new lifters and to install them out of the box. If the top of the engine is getting oil feed then here is what I have learned to do to help get lifters to pump up. It is messy but the vast majority of the time works. Run the engine with the valve cover off and put downward pressure on the pushrod end of the rocker. This helps the lifter bleed the air out and take a prime. Also some times all it takes is to run the engine and then shut it down and let sit for a few minutes, restart and the lifters have bled out and pump up on restart.