Lifter Bore Measurements

It's not that critical. Certainly not as critical as the machining on the bores and journals and the resulting clearances. I've run engines with a quantity of lifters with .003+ clearance with no issues with standard pumps. I've also run a standard pump on a block with .0015 clearance on the lifter bores, but with .003-.0032 oil clearnaces and the pressure was lower with that same std pump. Admittedly I drill the main feeds on every engine I do, so potentially I could be making the lower end more of an influence.

IMO - you don't need a HV oil pump unless the bearing clearances start getting big and the gaps on the rotating assembly are hemorrhaging a lot too. The lifter bores can hemorrhage a lot before you see an issue with delivery to the mains, unless the mains are letting a lot out with them.