Yes, I had figured that out, but the site has the smaller rifles mounted on the #2 as well. The 1864 manual doesn't seem to address the issue (the carriage section seems to have been slightly older/more tentative than the rest) but the difference in spacing between the trunnion plates in various drawings clears it up: the ~3" rifles, 6 pounder gun, and 12 pdr howitzer all have the same trunnion spacing, while the Napoleon is wider.