Igm270: if all you want is a pump rifle rebarrelled contact our sponsor MGM Barrels and see what they can/will do for you. Failing that run your question past gunnut69, our Gunsmithing Forum moderator. Also, The Montana Rifleman makes and installs fine quality barrels and I see no reason why they wouldn't wok on pump actions.
I think a 8mm pump is a good idea and would like to see one. Let me know how you do. Good luck. Mikey.