Need some info/help
[1] If the lifters are new, they should not have oil in them. Push down on the plunger, & without oil in them, you will get 0.125 - 0.180" of plunger movement. That is the pre-load available & the lifters can be set anywhere in that range. Some people like to set the PL 0.020", or a small amount, but that risks lifter pump up & popping out a circlip if the engine is over-revved.
[2] Lifters have oil in them. Compress a lifter in the vise slowly to get rid of the oil. Then, perform [1]
[3] Brand new lifters made in the last 25 yrs. Say a prayer to Allah that your set will not fail, because plenty have.....Safest lifters are 25 yr old ones that have been re-faced.....