I asked around at the local gun shops, and they recommended a smith in the next county.
As to the patterns, well, they're a lot better than they used to be with only the cylinder. Before the modification, I had to stand directly behind the trap house, with my box of shells sitting on it, in order to break targets. Not a desirable position to be in if others are shooting from 16 yards! So having choke tubes, any choke tubes, was a vast improvement.
But I wonder if the guy might have done something of a hatchet-job. When I run my finger into the barrel, there is a drastic 'lip', where the choke tube diameter exceeds the diameter of the barrel. I expected the two surfaces to mate flush, but it isn't so.
Of course, the smith didn't make the barrel or the tubes, so I don't see how he could have caused the lip. You're opinion here would be much appreciated, George.
As for patterning on paper, I haven't done too much of that, and only at very close ranges (under 15 yards), so I couldn't give a really informed opinion.
BTW, it cost me about $85 for the machining and three tubes. I've since bought Winchester extended tubes. They have about 1/4 inch of knurling beyond the muzzle, which eliminates the need for a tool for changing tubes. $12 each, if I remember correctly.
Ask around, or if you can afford it, send your barrel to that Vang Comp guy. He seems to be quite a miracle worker, from what I hear.