I have also ran into block's with oversize lifter bores. They usually have a small diamond on the lifter bore to indicate a oversize bore. But sometimes there just wore out. The cam bearing can lose a lot of oil by the by them too. Did you put any new ones in? Truth is you're inside of your engine is just a huge oil leak the tighter you can keep your tolerances the better you are but not too tight.
P.S what does your saying under your Avatar mean?