The 39 uses a 90 degree hold down bracket sort of like a 40 with a single bolt in the fire wall. Bob Drake has a good picture of the complete hold down assembly on his web page. Hope this helps you.
If I recall there is also a bolt through the inner fender skirt.
You can research this through pictures in the green parts book
but is more clearly pictured in the 39 parts book. G.M.
Here's a couple of pictures of cars I have done using NOS battery hold down parts. Hope this helps.
There is in fact a bolt that goes through the inner fender panel. If memory serves, that bolt is integral of the tray and a nut and washer are placed on the "wheel side" to fasten it appropriately. There is a also a piece of anti-squeak material placed between the tray and panel.
I'm also looking for information and or pictures of a battery hold down assembly for a "41 sedan. I presently have no hold down, but there is a bracket attached to the inner fender well forward of the battery tray that is not attached to anything. Help!