Compared to the square 6V batteries, the rectangular are much better sealed and crimped. I think with patience you could probably undo the crimp on the bottom of the battery if so desired. My eventual plan is to cut the bottom out of the batteries and extract the cells that way. I would then make a low profile access panel so that cells could be inserted and/or charged. This would be the least visually obtrusive method that I could come up with. With this approach, function is re-established and aesthetics are maintained. You just couldn't set it in a puddle unless the access panel was made water tight.
Oh, and for now I went ahead and ordered two of the batteries from Newark. When I initially looked into it, there was an additional shipping charge that was pretty hefty. When I went back after others had success, shipping was pretty normal. It seemed like the easiest solution for now. So, no steampunk battery made out of brass & copper sheet for now.