I've seen adjusters and pushrod cups broken off due to using to short of pushrods, way to short
To long can and may beat up the bottom of the rockers also so my choice is to see between 1/8 of a thread to three complete threads max exposed under the rocker arms
As already mention on the single shaft T&D system they like 1 1/2 turns out to three turns out max on their adjusters for oiling the push rods properly
I think I have 1 1/2 threads exposed on my 440-1 with the Jesel pair shaft system with pushrod and spray bar oiling