Hi Mike,
If you are going to shoot that beauty, try 79 gr. by volume of Goex or Scheutzen 2F B.P, and 1 1/16 oz of nickel-plated shot from Ballistic Products, using a good wad column. My old pitted barrels (most are) don't care for the cheap fiber wads and prefer something with a better seal such as a .125 thick "nitro" card plus two Wonder Wads - at least one of them lubed. Or simply two WWs. I don't use plastic wads in old barrels, both to keep pressure low and to avoid plastic fouling in the pits.

I have done a LOT of patterning with old pitted barrels and find the nickel plated shot well worth the cost: 8-9% better patterns and far better penetration on game - especially the feathered type. NP 6s will penetrate as well as lead 4s or 5s. For ducks, No. 4 Bismuth is fine in old barrels.

Aloha, Ka'imiloa