You can measure that bit of journal ahead of the trunnion.
They aren't going to select you a barrel at a vender based on that though I don't think.
See what it is if it's 907 or under you should be fine ordering any barrel.
I don't care to work with nitride to much I think it's super hard on end mills. But a lot of people seem to like them.
I was thinking there was chrome lined US barrels available too.