Match drilled mounting bracket to battery tray rivet holes. Deburred, dimpled and riveted brackets to the tray. Match drilled battery hold-down bar to mounting bracket and installed nut-plates.
I made a few minor mistakes, but it will work okay. I let one of the mounting brackets move while I was match drilling. I didn't center the bar that secures the battery when I was match drilling it. I tried different orientations of the bar and tray and found one where the errors cancel out. I may need to make longer spacers for the battery hold-down bar.
I sanded off the rough edges of the battery lightening holes using a small drum sander in a drill press.
I test fit the battery tray assembly on the firewall and and will drill those holes tomorrow.