Barrels interchange on the Beretta A300 (the original A300, not the new A300 Outlander), A301, A302, A303, AL-1, AL-2, AL-3, Browning B-80, Breda Altair (older Italian Altair, not the newer Turkish Altair), and Singer Nikko Gas Auto. The Beretta A390 and A3901 barrels can be modified to fit the older models.
I looked at the Al1 today. I was very surprised that it's a new in box (box shows the Garcia Tackle Co. logo as well) with all the manuals & paperwork. Looks like it has never been assembled. Any idea what one in this condition would be worth?