Yes - I second Alan's findings - converting double shotguns to fire round balls is as easy as cutting the barrels behind the chokes, filling in the hollow centre rib if necessary, filing the rib to take sights, standard 3/8" dovetails are easiest and working from established shot loads. Round balls from smoothbores shoot best if bore size or slightly under size, with a shot-cup base wad, placed cup-up underneath the ball. A shot wad has a cupped base wad attached. This is cut off and used cup-up underneath the ball to help centre the ball as it travels up the bore. This system has worked for me giving excellent results. The below is the order of placing wads in the hull.
& means powder
= means overpowder wad/s
( is the gas check wad, cup-up underneath the ball
} is the top wad or fold crimp which is what I use

; So this system is powder $ then wads = then ball centering wad ( then crimp }.

If you want to develop black powder loads to find what a REAL 10 bore was like to shoot with round ball, merely pour a 2 7/8" 10 bore hull with 200gr. of 1F GOEX or 2F GOEX powder, then place a card wad over the black powder powder, then the gas check wad part of a shot-wad underneath the ball, then crimp You adjust the wad height with card or fibre wads to get the correct height for a crimp, just as you would if loading shot. This is just a moderate load, 7.4 drams. A full BP load might be around 9 or 10 drams. There are 27.3grains in a dram.

I use Jeff Tanner's moulds in my 12 bore round ball guns.
You should measure your bore before ordering a mould. You will need a set of RCBS or Lyman handles.