You might take a look at this one: https://www.gunbroker.com/item/888682043 If you can do the stock repairs, and if the barrel is OK, it would give you a chance to get your feet wet with an 8 gauge. If you have to replace the barrel, The Gun Works could probably do the work (though you'd have to make a decision on rifled or smooth).

There's also a W&C Scott double 10, but from the photos the barrels worry me. Shame, as it was once a nice gun.

If you've got someone who can fix the action and replace the extractor, this one might be a good candidate for shooting ball from cartridge: https://www.gunbroker.com/item/886875562

Around here, prices for original ML doubles peak in the 12-20 range. No one wants a 22 or 24 gauge, and no one wants anything bigger than a 12 since you can't use steel shot in them. Prices rise again at 8 gauge, and a 4 gauge would probably go for 4-5x an equivalent 12 gauge. Almost no one shoots ball in them more than once or twice as a novelty.

For me, my 11 gauge is perfect. Heavier--thicker barrel walls--than Pedersoli's 10 gauge, but I ain't wingshooting with it. It patterns OK with bismuth shot, if I feel the need to hunt waterfowl (which hasn't happened in a decade, so I think I'm safe). It does go through a lot of powder and lead.

If I decide I can no longer live with the current barrel length, I can shorten it with a clear conscience. It has no provenance, and isn't a collector's piece. I'm going to look at a couple more tomorrow or Friday, I'll see if any look good for your project and get contact info in case you decide you want it.