This has been a dream of mine as well. A few years back I found a company that machined the 7600 barrel extension and imported them into Canada (not sure if they still exist and can't recall their name at the moment). They included part drawings and a how to install and head space the new barrel extension correctly to your new barrel. I'm pretty sure I squirreled that info away at home somewhere. I'll have a look tonight and get back here with some more info.
I guess the issue with attempting a re-barrel is that quite often the original barrel extension will get damaged upon removal and can't be re-used. The solution is to install a new extension onto the new barrel and simply swap it on the action. Anyone who has stripped down a 760 or 7600 knows this can be done relatively quickly with simple tools. As long as you stick with a family of cartridges that share the same head diameter you could run multiple barrels off the same action! And swap them in the field in minutes!
(sight in required obviously)
I wanted to set up a 22-250 and a 6x55 or 7x57 to cover coyote and deer/elk/moose hunting but never got around to purchasing a 7600.... yet.