Gawd Simon, you don't have much luck with your engines, do you??
I am unsure about the collapsed lifter theory, since even if fully "bled down" there should still be some valve lift left. I rather suspect that you have some cam lobe issues there.
If the valve train is "ajdustable", try checking that first.
Was there
oil in the enigne when you got it? Was there any metallic debris in it whne you drained it? Also try cutting open your (old)
oil filter to see what it has trapped.
Any other valve train dmage you can see? Broken valve springs, bent pushrods, "bent" rockers etc?
Get this pinned down before you even think of firing that engine up.