Craig, the end result is to have the oil entering the cylinder bellow the oil control ring/scraper regardless of piston type/make.....You are correct if you say you have found the hole feeding into or above the oil ring.....this is a mistake that I have found on many cylinders from old days. I have even plugged off some of these holes and redrilled new ones lower down the bore. You need to measure very accurately before you start drilling. I put the piston in the bore minus the rings and at bottom dead center, mark the rear of the bore with a fine texter pen or pencil, and measure down from there to just bellow the oil ring. Then transpose the distance from the inside of the liner to the outside. Drilling the hole at a 50 degree angle just makes the outer hole on the outside of the liner slightly higher so as to align with the crankcase gallery. I just use a dremel to cut a groove vertically to achieve the final passage way. It doesn't have to be anything fancy to achieve a good result. If the liner is too loose a fit in the case spigot, some oil loss around this area will happen. I always use some sealant on the base gasket no matter what. If it's an old engine, no matter what it is, you can be sure it will try and leak if you do not do all that is possible to stop it. Good luck........Greg.
) so the only thing that gets blocked with muck nowadays are the petrol pipes.