Lonnie,
The bolts on all my '54 battery trays were attached with two heavy rivets per bolt. I used threaded stainless steel rod as described by Jerry but a I ground the threads off on two sides at the bottom of the rod, drilled holes in the flat metal, and attached the rods to the tray with flat-capped machine screws (so they looked like rivets from the outside). You could do the same with long bolts, buy cutting the heads off; grinding the non-threaded "base" flat; and, then attach each bolt to the tray.
Hooked bolts (as described by Jerry) were used from 1955 onwards (J-bolts).
Or,
replace the whole battery-tray assembly (which includes the bolts). Tim
