Alright, for all you research hounds' out there, here's a golden question. How much vertical adjustment was there for hub guns'? I ask because not only do you have to figure for the hole in the spinner, but also how much room is there physically for the gun's breech-end to drop, so that you can actually get the elevation required for something like a D600 convergence? Alot of planes' that have hub guns, have them mounted in the Vee between cylinder banks, and being as the hub guns' were usually cannon, They would most likely be large enough to take up whatever room there was, even if they were installed flat (without any elevation.) Anyone ever looked into this subject? It might be that you had no elevation through setting for distance. Maybe these guns' historically fired flat, and the pilot had to make the correction?