So I have an older model Colt Trooper .357 with a 6" barrel and am wanting to change the barrel on it to an 8 inch. I have found a barrel for a good price but it is from a colt trooper "mark III". Will the mark III barrel fit my older Trooper or is there a big difference in fitment? I'm not trying to pass it off as something that it's not but just looking to change the barrel because the one that is on it has some pitting issues. Any advice would be appreciated.