3/8"-16x3/4" socket heads work neatly for the clutch cover - that's what I use.
Take one of your flywheel screws to a fastener house, or something like Quality Farm & Fleet (or other farm equipment parts supplier) and ask for a "place bolt" of the same size.
And give me the length under the head, if/when you pull one, please! I know the threads are 1/2"-20, but I need to confirm the length (probably around 5/8"-3/4", but I want to be sure. The flexplate screws are .590" long, and the flywheel screws should be a bit longer.)