Not too long ago I looked at converting a Savage 10 (short action) in 308 to a 300 WSM. I determined that along with the magazine & follower, I would need to change the bolt head and baffle over to the CRF version. Savage puts the ejector for this in a little cut in the receiver (I guess there's no room for it in the bolt face when you go from PF to CRF), so I lined up a smith to do the work.
Next issue will be the barrel. Except for some early production runs, the savage 300WSMs are in what's called a "Large Shank" - that's the size of the part of the barrel that screws into the action. However, your action will most very likely be a "Small Shank". You will probably have a hard time finding the barrel, so you will have to look at a custom barrel.
Well, net is by the time I did the math, I was about $200 or so short of just buying a new rifle. New savages go for between $450 and $600 for a hunting gun. So that't what I did - just bought a new one, savage had already figured out the details ;)
Dunno if you would have the same problem converting to a 7mm.
Check out www.savageshooters.com
. You might have to join to get to the answers you want (like $12/yr), but all the info is there. Lots of handy reference posts.