Since the Slanty oils hydros from the top down w/dedicated rockers & hollow pushrods(ball&ball ends), they can't just be "swapped in" like an A-LA-B-RB-Magnum-Hemi, so not knowing who-what-&where it's remotely possible. They could drop the Hy cam & lifters in, set the pre-load, and not realize there will be no oil to the tappets.