If your worried where to put the Unertl front mount it's 7.2 inches from the center of your back mount. Measure from the center of the adjustment screws. If you don't have that exact gap when you are shooting the rifle and making adjustments they won't be by correct increments. Good luck. Unless your going to compete (where they do not allow it) I would leave the recoil spring on, But that's simply a matter of opinion. I believe it was designed with one for an obvious reason. The USMC had an unlimited budget. They weren't concerned about having to replace the scope. As far as the hand guard I would try and locate the correct one. Or as suggested cut it too fit the ring.