A solid battery tray is no good without an equally-solid hold-down.
The original T-bolts were used. One of the T-bolts had broken, and had been welded back together with globs of cold MIG wire. The bolt almost broke in two under hand pressure. I ground out the cold welds one side at a time and re-welded them. We found more goofiness in that one of the T-bolts was an SAE thread, and the other was metric. This would have been the right time to replace the bolts, but we decided it was OK to retain the existing bolts as long as we didn't mix up the nuts.
The upper hold-down bracket was made using angle iron, flat bar, and a pair of pre-stamped tabs.
Short sections of 3/4-inch tubing were welded to the sides of the battery tray to give the lower ends of the T-bolts a home.
The fabrication was done at this point. It's time to get a protective coating on these new parts and get them installed.