Jack, The subject of barrel interchangeability is a multi faceted one. First I would think that frame size is of primary importance. IE: 1 1/2 frame barrels to a 1 1/2 gun. Also if I was looking to fit an orphaned set of barrels to my gun I would try to find a set somewhere close to my serial range. The main reason for this would be so that the bolt and corresponding bite in the barrels would be a better match. Parker went to a replacable bite around 1905 or sum such. The 12 1/2 degree angle of the locking bolt was consistent through production.
I don,t really think that fluid steel or damascus plays into whether a particular set would fit or not. Being that these guns where machine made and hand fitted I think that you would have to count on some type of fitting.
I have seen a few guns where another set of barrels have snaped right on but they are few and far between.
1) frame size
2) correct bolt variation
3) dolls head
4) ejector gun or extractor gun
I am sure some of the other guys will chime in here but I hope I have at least started the thought process
