You already have your PAC springs, correct? You have chosen a Lunati cam, correct? You are asking about Schubeck lifters, correct? Sounds like 'cobbling' to me. Usually you choose the cam first, then use the springs and lifters recommended for the cam. What spring specs does the cam call for? Those springs will probably work but why rely on a guess? Call Lunati, see what thy say.
I thought the Schubeck lifters were disco'd too, but I guess not.
As I understand it, most use/used them because they can be used with different cams without issue. If you're messing with cams all the time, it keeps costs down (after the large initial investment) and makes installation easier. But, if you're building one motor and don't plan on swapping cams every week, just get the lifters that should be used with the cam. Schubeck lifters were really expensive too, no? Like $900? How many sets of lifters could you buy for over 900 bones?