The fitting on the bottom of the crankcase is the crankcase breather. Either leave it alone or if you are compelled, put a piece of tubing on it and run it outside the cowl.

Four strokes present a couple of problems being inverted. One is tank height. It must be centered on the needle valve. The second is that you no longer have an updraft carb but a down draft one. They will often flood easily when inverted.

Other than that run it just like your 2 strokes with the same fuel.

Use a 14-6 or 13-8 prop and a OS 'F' plug.

Enjoy,

Jim