I think you are worrying unduly about oil levels, you have drained the oil tank and the sump so you have virtually drained all the oil out of the engine. When you put fresh oil in up to the level I have suggested 1/4" below the return hole in the tank that is the correct starting level. When you start the bike the first thing to check is, as has been stated is to check that oil is returning assuming oil is returning then after running the bike for a few minutes and you stop the engine then recheck the oil level it will probably be slightly below the previous level this is because oil is now filling the oil ways and there will always be a small amount of oil left in the sump and you should then top up to the correct level but no higher. One other thing that you might want to check is if the bike is left standing for say a week without running then before you start the engine check the oil level, if it has dropped more than say 1/4" then your bike is suffering from what is termed as wet sumping, and oil is draining into the sump it maybe worthwhile draining the sump before starting the engine or if you do start it, it could pump that oil out through the breather onto the ground. Wet sumping is a common thing on old bikes I have 2 bikes one wet sumps and the other does not so if I start the bike that wet sumps once a week I have no problems but if I left it for 2 weeks then when started it would pump that excess sump oil out onto the garage floor.