[Dwight Southerland]

If you are not using a new CNC'd block (GMPP. Dart, etc.), there are multiple advantages of bushing the lifter bores. 1) Blocks from the 1960s are notoriously out of register. Having the lifter bores correctly aligned will eliminate potential vale train problems. 2) The bushings allow for tighter clearances, thus more accurate movement. 3) Less wear 4) You can restrict the amount of oil to the top end easily, thus allowing more oiling to the camshaft bearings.

If you are concerned about oiling the camshaft-lifter surface, you could have a vertical groove from the galley hole to the bottom of the bore.