My guess on why the flywheel cover is missing is because it rusted out and someone tossed. The covers tend to collect a lot of grease/dirt that holds water and the covers rust out from the inside out. I had to throw mine in the trash. Bought one off Ebay and after media blasting was only marginally better. There should be two covers...one is more of a plate (vertical) and one a bowl (horizontal/bottom).

Good luck with your project.