From what I see the problem comes from the valvetrain in the first place. Something dropped from there and was picked up by the
oil pump and seized it, leading to the broken
oil pump shaft and the
oil starvation and everything else thereafter.
Basically the studs for the rockers are too short or the pedestals on the heads wrongly machined . Maybe these rockers are not designed for these heads.
The stud barely engages the adjusting nut, the rockers sit too low on the head , the pushrods are probably too short and the valve retainers probably touch the rocker sometime during their travel.
The valve springs need be much stiffer for hydraulic lifters, because the heavier weight needs additional force to push them fast enough towards the cam lobe at high revs and prevent the pushrods from banging around and jumping out of its place, which is probably what happened and made the lifters break.
If the rocker studs are so bad off, I would suppose that the valve springs were badly chosen also.
If you look at the picture in this link
http://www.racecar2000.com/ad-photos/44758-mod.jpgyou will see a Windsor 406, and the stud clearly sticks out of the adjusting nut and the rockers have much more space in relation to the retainers.
I would really like to know what the engine builder has to say to this. This is a perfectly botched job and a clear Warranty case, and the engine would have to be repaired by whoever built it at no cost to Andronikos.
Of course, there is allways the possibility that the previous owner did install this UPGRADE.