Here's an update on my question. It's for general info for those faced with the choosing among battery replacement options.
I took the upper retainer for the battery to my local MBZ dealer to see if it would fit squarely on battery no. 000-982-31-08 which is the recommended modern era substitute. It did not. The battery is slightly longer so this is not a good replacement option if you want to use the upper retaining frame.
However, I did find a non-MBZ battery that fit well. I looked at Interstate's MT-24F. It was a very good fit to the upper retainer. This was recommended to my by Bud's Benz.
The original MBZ battery is a long delivery item, so the above Interstate option may be a good compromise.