I looked at several Winchester catalogs and some Stoeger's but didn't find anything mentioning special order barrel lengths. It is possible that it could be a factory "special order" as Winchester wanted to please customers if it was feasible. I would first suggest that you have a gunsmith check the choking of the barrel to see if it has any. If it had been a 26" barrel I doubt it would have much, if any, constriction left at all. If it does have real original factory WS-1 choke that should be a positive indication to pursue more information. If not....
I am certainly no expert but I have owned several MOD 50 20ga shotguns mostly with Win. vent ribs. On inspecting my 20ga Mod 50 vent rib barrel, I found that the rib posts occur at exact 2" intervals starting from the muzzle going back to the receiver. From that, I would say it would not be a difficult task to cut both the rib and barrel to 22" (or 24" or 20") and dress up the cutting. I think the factory probably cut the barrel and rib separately and then joined them. However, if the barrel and rib were cut off after it left the factory (with the rib left on when it was cut) the fit of the rib with the post at the muzzle might either overhang the post or be perfectly flush with that post. The one's that I've seen show the slight bevel of the post at the edges and no evidence of the post being cut vertically. It would be helpful if you could compare the rib/muzzle fit of your barrel with one that is known to be factory original. There. A very long answer to a logical and simple question. I really like Model 50 20ga's. I think a 22" barrel would be a super fast-handling quail gun for sure. I hope someone more knowledgeable than I can give some better info. In any case sure hope you like yours too.