Drain all of your liquids, before you turn it upside down. Take the oil pan off, and clean it? I'm thinking this because, my oil pan looks like hell. Anything heavy (That's including parts of a gasket I found in my oil pan) will sink to the bottom. If you invert the motor before you clean the pan, parts of crap could easily gut into the rest of the important bits. Remove and clean the oil pan, replace (New gasket may be needed) then invert. Plus a few rags under the engine, or a piece of cardboard. To prevent oil drips on your floor.
If you drain the fluids, and invert you should be fine. I'm just thinking out loud.
