The Z-hat link's sights look about right and the same as the one I bought from Brownells in 1986. The one I got was 3 leaves + one standing, for 4 sights total - not needed for a 12 gaube smoothbore.

I suggest 2 at most for a 12 - but then, a single is all that's really needed. If shooting slugs, you'll need an 'extra' leaf for the same effective range as round balls, due to the drop experienced.

With a 1,500fps load, black or smokeless (smokeless kicks about 1/2 as much), and sighted 1" high at 50 yards, the balls will strike on zero at 78yards and be only 2.3" low at 100 yards. 100yards is about the max range for a 12 bore smoothbore for deer, moose or elk.

With rifled tubes, I'd go with a standing sight and single leaf, giving 80 yard zero, and 125 yard zero. That should cover effective range for open sights.

The gun and cases will actually handle round balls to about 1,800fps to 1,900fps, if you want that sort of recoil and would really flatten the trajectory.

At 1,900fps, the ball's trajectory is as follows - 1.1" high at 50 yards, 1.1" high at 75 yards, 0 at 100 yards, and 2.6" low at 125 yards, thus 100 and 150 yards would be good zero ranges. Zero'd at 150, it's 3" high at 125 and 5" low at 175yards.
As far as energy goes, 4,368 at muzzle, 3,528 at 25 yards and 1,852 at 100. The BC is .089, by the way.

This is with a .715" pure lead ball only, at 1 1/4oz.