Mike Orlen, among others, can install permanent choke tubes. If there is any wall thickness left at the muzzle, that will get you as much choke as you want. I think Mike sweats or solders the chokes, but I have seen an article by another smith who installs them with a permanent bonder (black LocTite, I think). I can find his name if you need it. These are less visible than the flush thinwalls.