Yep, I have seen the different ways of mounting the bipod too.  My thoughts on the matter stems from an old guy who was in the Army in early Sixties and he told me the bipods were originally installed forward towards the muzzle and pulled to the rear to deploy.  He also said that not too many of these stocks were fielded and at a certain point it became a matter of did you have a bipod and is the sling set so you don't break the handle off.  He has since moved on the Great Gun Range in the Sky.

Happy Shooting!