Hi Ed. The twist in mine was 56", seems to me and about .008" rifling depth. Dang- might have been 48", though. Na - 56", an older rifle from the 1980's.
I deepened the cups as well as shortened the nipples. Must watch, that the main spring doesn't crack the wood out below the locks, so there are limits as to how much lowering (= more spring travel) is done.
I would be very edgy about shooting slugs in a SxS - concerning the movement of the other barrels slug on recoil, creating a space between powder and slug.
Too, of course, just not needed.
As noted, I started off with a LEE DC mould and then switched to the Lyman .570" Which actually cast .574" X .574".

What surprised me about the shiny locks and trigger guard, is they took cold blue and turned very dark for me, as you can see in the bottom picture.

Oh yeah- forgot to mention. There was a 1 pound bar of lead inside the butt. It started rattling as I was sanding the stock, prior to refinishing it. The vibration of the orbital sander, loosened the lead so I was easily able to remove it.
I much -refer slightly heavy barrels and the 1pound lighter gun. It was already almost 9 1/2 pounds without the lead, just about perfect for a hunting rifle, imho. That is what my .69 weighs.

Wayne, sometimes they can be really difficult. A friend of mine who had one, a .58 like mine, shot only slugs in it and the closest he got them, was about 10" at 50 yards. Useless, as far as I could tell.