I used to own an Ithica "RoadBLocker"; 10GA, tube fed semi auto.
I've never seen one with a box mag nor is one listed in my copy
off Fighting shotguns. There were a few 870s and full auto Remington 1100s made in the 70s with box mags. All of these were experimental and belonged to the government.
If you find a box fed Road Blocker it must be a custom job. Fifteen round magazine, must look like one for an AA gun. I'd want it tripod mounted. The gun itself is heavy enough.
Everyone should be given a Bible, a boyscout manual and a Swiss Army knife at birth. All life's problems can be solved with these tools.