hose from oil breather to air cleaner on 383

Yes both full marks are just short of 20” looks like your stick is on par. Are you using the correct tube as pictured. Overall Length should not really matter just the full mark location. The add marks are a bit different and do not know if add is a quart, or 1/2 quart?

Is the windage tray installed? It might reduce about 3/16 for the full mark if the tray and second gasket is not installed.