I've set the lifter pre-load godonlyknows how many times while setting the valve timing on shovelheads. What kind of lifters do the new Enfields have.
(I know I know Look it up!)
The UCE, including GT, have what appears to be Delphi(or similar) hydraulic lifters with a .750" wheel.
Preload should be about .020".
Unfortunately, there are no adjusters provided. The only ways would be changing pushrods length or shaving the barrel.
However, on our Ace GT Billet head, we do provide adjusters on our roller rockers, so they could be set correctly with our heads.