Since the pinion shaft and bushing are the differences between end and side oiling, I don't believe there is any way to convert without replacing at least the bushing. The bushing has to be changed to have a passage to the end of the shaft instead of a hole through the wall, and the shaft has to be changed to have the hole in the end instead of in the side. Some pinion shafts have a threaded plug in the end that can be removed to allow oil to enter there as well as through the side, so you might be able to just replace the bushing with an updated one. You would get better oiling to the crank pin and loss through the original side oil hole would be minimal. If everything is new and tight you will be OK doing this. I don't usually recommend replacing just one bearing on an assembly though, as the difference in clearances can cause issues. I learned this by snapping a crank pin completely in half due to new main bearings and old pinion bushing. Bushing was in tolerance, but loose, and main bearings were new and tight. Just under 5,000 miles to a snapped off pinion shaft. 200 miles from home on the side of the road.
