RE: Screamin' Demon cowl plug #2 - nearly done!
If you make the cowl relatively light it will hold up everywhere else, but the screw hole area needs to have extra layers so that the build up is at least 1/16" Sleeving the holes with little hunks of brass tubing might also keep the screw from crushing and digging into the cowl. Notice that the German planes might have wire hoops to stabilize the cowls.