Remembering off the top of my head the gap is just under 23mm, maybe 22.8, but that leaves no room for chassis flex so you'd want to be lower again.
I've got round it by simply mounting the cells further out so they don't touch the bulkhead, but this does mean you can't use cells with locator bumps on
Unless you can run them upside down, not sure!?
Oh, you also need spacers under the battery posts to raise them as well, and I found it a very tight fit length wise!
Dave