Second the kudos for your fine pictures and good work. Printed those puppies off to put with shotgun load manual AND saved files to computer. Now just need to wrap up load workup for 32 acp so I can move onto working on these with more focus.
I would guess most of my loads would be RB or maybe the Lyman 20 gauge slug, with the Lyman Minnie bullet mixed in to at least try out.
I know I mentioned rifled choke tube before, only one I have found online is this Carlson's extended tube https://www.midwayusa.com/product/10...20-gauge-black with 1:35 twist rate.
I was also looking at cylinder bore choke tube. Lower cost and absent a scope (not pre-drilled) or rifle sights on a replacement barrel I'm not sure I will get more value out of a rifled choke. Won't be able to aim past 50 yards if that far just using a bead sight so... At $16 it certainly is an inexpensive way to allow shooting RB, Minnie, and slugs. https://www.midwayusa.com/product/28...choke-20-gauge
On the other hand more accurate at 50 yards is still more accurate.