Originally popular as glass-ons in the 1960's, now "D” fins sometimes need to be put in fin boxes, True Ames has done it. The larger area on these fins allows for harder turning and easier nose riding. Try one on your log and take a trip to the past.
This will just fit in the 10” standard fin box because they have made an overhang in the rear of the fin. You may have to take out your “fin box leg rope” but mostly we know D-fin riders do not use such newfangled attachments anyway.