I had a similar gun - British victory model with cylinder holes reamed out to accept 38 specials. It shot 38 specials ok except for the bulged cases. I replaced the original cylinder with a 38 special cylinder and it still shoots fine and cases extract easily now. The cylinder I used was from a later revolver. I used the extractor parts from the original cylinder.

There are lots of "parts kits" available now as police departments specify that their trade in guns be cut up. If you can find a cylinder from a cut-up 38 special victory you are in business.

Here's a parts kit: Smith & Wesson Victory parts kit - Gun Parts Kits at GunBroker.com : 796981337