kombi - gee, that sounds like a decent deal. I would go for it. I know what you mean about not having a great love for cut down military stocks - they don't seem to molify the recoil as much as a nice walnut stock does. And, Boyd's has some pretty decent semi-finished large ring Mauser stocks for about $70 (US), which is a pretty good price.
As for the 7mm vs the 8mm - well now, this is a matter of significant import. The range of bullet weights in the 7mm usually goes from about 120 to 175, with a 140 being what a lot fo folk use. The 175 however, from that 7x57, is a world renowned game getter. The 8mm bullet weights usually range from about 130 (I think) or 150, to 220, with the average being either a 170 or 185 yet some of the better hitting stuff is in the 196-200 grain range. And that cartridge too has been as successful as the 7mm.
Here's what I would do, but this is just me.... See if that 8mm shoots - if it does, leave it and enjoy it. If the barrel is shot and she won't group for you, even after being bedded and scoped, then re-barrel to 7mm and enjoy it even more. HTH. Mikey.