Here's what the repair looked like from the top side, after pulling the plastic bag and cardboard off. You can see one of the rivet hole stress cracks on the upper right rivet hole.
And after some preliminary trimming and sanding. Once I got the underside flat, I used the busted shaker as a stencil, placing the two, flange to flange and traced the correct curve with a pencil onto the new shaker dome's underside.
