On hydraulic flat tappet I never bleed the lifters, I find it easier with them pumped up. What the other members have said is correct, yes you can reuse, a cam upgrade would be better but depends on intended use. Myself, I use the old school method to set the rockers on hydraulic flat tappet lifters, which is what I think you were asking, since you have adjustable rockers, Back them all the way out, install everything, Start at number one cylinder, cam lobe in the closed position, then simply take one hand place thumb and index finger on the pushrod, turn the pushrod ever so slightly back and forth, while at the same time slowly tightening the rocker adjuster. Soon as you feel the pushrod stop, stop right there and turn the adjuster another 3/4 of a turn, done. Do that to all.
Now if the lifters bleed down, or you keep turning after you have reached pushrod seat, you will force bleed down the lifter. Be careful with this because you can go to far, and valve might not seat or piston to valve contact could occur Once the lifter pumps up. This is why I like them pumped up, you get more of a solid stop when the pushrod seats. So if they bleed down or you feel you wend too far, no sweat, back off the adjuster, try again, but this time the lifter is not pumped up, so repeat the steps above, soon as you feel a drag, stop because bleed down lifters won’t stop the pushrod from turning like a pumped up lifter would. With your fingers try to move the pushrod up and down, jostle it around a bit with your fingers to check that it is seated and there is no play. If it doesn’t move up down or side to side your good, now turn it 3/4 turn on the adjuster. Done.
As always when done check where your rocker is touching the valve stem, you want it as close to the middle as possible, you can check this by sight at the side, or use chalk to find the wear pattern. If it’s touching on the top of the valve towards the intake the pushrod is too short, if it’s touching Towards the bottom of the valve stem towards exhaust manifold, the pushrod is too long. Middle is just right. Though should not be an issue unless something has changed, like shaved heads etc. If pushrod length is incorrect you will need to measure for correct pushrod length as Moparofficial said.
