There are two of four brass fitting which inject oil into the case, in line with each connecting rod on the crank, when the pistons and cylinders are connected, the rods will not touch these fittings, where they protrude into the crankcase. But without the top end attached these rods can flop around and damage these fittings, causing a restriction in oil flow into the case, when reassembled.
You can dremmel these fittings flush with the crankcase, re-chamfer the holes, blow it out, and volla, no need to worry anymore about them being damaged during your rebuild.
Good Luck!