Working class choppers, Ithink that much case cut off will effect how the clutch works. Not enough strenght to keep the cover from flexing. To much flex to take up before the clutch starts to work, then not enough travel left to work clutch.
I use some nuts as spacers on the cover. The nuts use a ten mm wrench, one thin, one thick. Longer screws to match of course. Lets in much air to keep cool. Excess heat is not good for the alternator.
Leo