As for the marks, I believe that at some point in time, someone glass bedded the action with acra-glass, and then couldn't get the action out of the stock (got them stuck together). So, they banged and banged on the receiver with a small hammer or two, trying to get it loose, and putting the dents in it.
Another possibility is that they used a large monkeywrench (like you would use on a water pipe) to unscrew the action from the original barrel. I have actually seen old gunsmithing books where they tell you how to do this. But, the action has to be heavily padded with leather before you put the wrench on it, or the wrench will cut marks into the action.
Sadly, I agree with the prior poster. The .308 Winchester is a 66,000 psi round, and you are firing it in a 100 year old action specifically designed to handle a 45,000 psi round. It will not take long before you get lug set back and a ruined action. I think that you should strongly consider hand loading the .308 rounds down to a low level load, giving perhaps mild .300 Savage type performance, to reduce the pressure in your rifle. And, I would only do this after first, once again, specifically having the headspaced checked by a gunsmith.
About 12 years ago, the second incarnation of the Kimber company bought up a bunch of old Swedes (a few thousand), put 7.62 Nato barrels on them, dropped them into sloppy black Ramline Stocks, and sold them under the name of the "Kimber-Swede." Several technical guys at Kimber were so outraged at this, that they quit! If you look back through the old Shooter's Bibles, you will see these listed for one or two years.
Regards,
Mannyrock