I can't see the bolt handle, but the scope appears to be mounted low enough that there must have been an alteration there, too. If that is the case, stock length should be of minimal importance.

I have a 7X57 Mauser built on a G33/40 action which was intended for my (then) girl friend, who accompanied me on my last trip to Africa. She decided not to hunt, and I ended up taking several head of plains game with it, myself, including a record book Peter's gazelle. The stock has about a 13" pull, and although I usually shoot with a 14 1/2" pull, I never noticed the difference. As a matter of fact, I killed a deer with it on opening day this year. Shooting with heavy clothes on made the short stock comfortable.

I realize the .318 WR has considerably more recoil than a 7X57, but you might give it a try. A trick I have used with shotguns which were stocked too short is to put my left hand out further on the foreend. Of course, that won't be much help, if you end up hitting yourself in the eyebrow with the scope.

I don't think it makes much difference what kind of spacer you use: a spacer is a spacer, but I have seen some wood spacers so cleverly matched that they were hard to detect, particularly on a straight grained butt stock, which this one appears to be.