How long will this little buz saw engine last.

If you look at the last two lifter bores at the back of the block(one on each side) they are drilled and tapped at a different angle. My thinking is, after who ever bushed the lifter bores drill through to the oil galley to feed oil to the lifters. Then tapped the outside holes hole and put the set screws in to plug the oil leak to the valley. Could be way off but that was my first thought.