I picked up a C39 pretty cheap and was wondering if Fostechs Bumpski would fit? I've been reading up and it seems a lot of stocks don't really fit em. Any help is appreciated.

C39 has a milled double-tang receiver. I don't see a Bumpski made for milled receivers, so you'll need to seriously modify either the gun or the stock. I'm not sure you'd be able to mod the stock to keep the lower tang, so you'd at least have to get rid of that. I'm not sure about the upper tang and whether or not you'd be able to keep that.

My 2 cents; don't bother removing either of the tangs unless you are absolutely sure you'll keep the bumpski, or if you have an alternative in case you change your mind later. Removing a tang with a dremel is easy, but welding or riveting a new one on is a bitch unless you've got the tools and knowhow or friends that do.