I expect you'd best get used to the idea of some trial and error to find out what powder, patch, ball loads work best for you. Also, be on the lookout for a micrometer or calipers to allow measurement of ball diameters and cloth thickness.
The Curly G. gun may be a 12 gauge, nominally .75 caliber. I've read Gostomski made some smoothbores in 12 ga.
For the Curly gun, I'd take some of the patches and try to find some material that feels about the same thickness. For starting powder load, 70 gr of 2Fg, and work up from there in 5 gr increments to maybe 90 gr.
I have a .62 rifled Caywood flinter. For hunting, I use 90 gr of 2Fg, a .595 RB, and some 0.015 oiled linen, and it's a fairly tight fit. Your .62 might shoot best with a .590 ball and a thicker patch, or even a .600 ball and thicker patch than I use - so trial and error is apt to come into play.
When you get to shooting each gun, retrieve some fired patches from downrange and look for signs of burnout or cutting. The patches, ideally, would almost look good enough to blow the dirt off them and shoot again. If they're 'blown', vary the ball diameter and patch thickness until you find an accurate combo that loads snugly and maintains the patch integrity. Good luck. SCL