The problem you will have is replacing the stock,if your wanting to retain the removable magazine. Nobody makes a replacement stock for those old side button magazine releases.
You should buy a blind magazine box for a 300 WM,and see if it will fit on your action. If it will,then any of the aftermarket stocks will be able to work for you.
I have everything you need to change to a Left Handed 300 WM,I turned mine into a 6.5-06,and have all the 300 WM bolt and magazine parts,as well as two 300 WM barrels. One is the factory 24" matte blued varmint contour,and the other is a stainless steel 25+" heavy sporter contour with a threaded muzzle for a muzzle brake or a suppressor. I also have the Go - No Go gauges for that caliber that I could sell you as a complete package for everything,as well as a set of Lee deluxe dies,and 300 WM brass.
Let me know if you would be interested in buying everything,and I'll get a price to you for it.