Need some help. I have a Marlin 39A circa 1967. The outer mag tube has seen better days and will need to be replaced eventually. It uses an older style mag tube. I have on hand a new style ( post 1975) one. The spacing is a little longer where the inner tube locks in. has anyone modified the newer style tube to work in an old style one, or do I need to try and find a old style one? Any ideas would be appreciated.