Just a warning: Murphy's oil is a vegetable oil based wood moisturizer. It won't so much get the cosmo out of the wood as it will condition the top few layers of wood, and make THEM look good. Don't be surprised if, days, weeks, or even months down the road, the cosmoline trapped deep within the stock starts seeping out again.
If you've got an dishwasher at home, it's more than worth it to give it the oven cleaner treatment and then stick it in the dishwasher, with a nice coat of detergent on it. We treated an old Mosin stock this way a while back, ran it through the process 2 or 3 times, and the only giveaway that the stock was used were the minor dings and scratches in it.
After that, she'd be ready for whatever you want to put on her, murphys, linseed, teak oil, tung oil, old english, pledge, whatever.I like teak and tung oils personally. Teak if the wood needs darkening, tung if it looks good light. More of a hassle to work with than some other easy finish options, but the quality of a hand rubbed finish from either is equal, and often greater than that of a much more labour intensive finish(spray, dry, steel wool, spray, dry, steel wool, and so on)