I had a 20ga Repro at the time and thought about a 16ga barrel set. Called CSMC. They said the barrels would require some fitting, probably about a $3-400 operation. Didn't do it, but would also be interested in hearing from anyone who did.

I've looked at some of the original 16-20 sets, and in at least a couple cases, while the barrels do fit, they're a little less than perfect.