Before starting on the rear cover, you should complete the air guide since you may have to make some cuts in the casting that are not on the plans to get the air guide to fit. If you are making your own carb mount, you’ll want to review that page and finish most of the work on that as well to save yourself a little time later.
The air guide was made from a 125mm diameter by 300mm piece of Aluminum 7075-T6. I bought a stick of this long enough to make the front cover, crankcase, rear seal plate, air guide, impeller, and a few fixtures. The diameter was needed to accommodate the crankcase so I did end up wasting a little material on the other parts.
The carburetor mount was made from a 0.75″ x 1.3″ x 2.4″ piece of Aluminum 7075-T6, while the lock cylinder was made from Ø5/16″ yellow brass. I change the lock cylinder to a full split cotter, adjusted the outside perimeter of the carb mount to better match my rear cover casting, and reduced the size of the mounting studs to #10 to better fit the overall scale of the carb mount.