Use the wads that fit tightly in the hulls.

I'd use 2 7/8" hulls myself, if I could get them. The shorter hull might make for better grouping and easier wad loading. It's all a crap shoot until your able to test.

My 3 1/2" chambered Pump shoots very well using round balls and 2-3/4" hulls, so it's not much of a jump.

www.trackofthewolf.com has wads & lists the sizes was well.

Measure as best you can, the interior diameter of the shotshell, then buy the appropriate sized wad from a source like track or or Circle W,X,Y,Z, or whatever they are called.

I expect you might need 10 bore or maybe even 9 bore wads, not smaller ones - but you are the one with the measuring device & the hulls.