So, you would need several items for the optic tube to seat into the handle housing. There is a diagram in another post just a few spots down in this same forum thread.
You would need the rubber donuts, Snap ring, resistance screws and a few metal donuts. Then you would need to find elevation and windage screws as well. And lastly you would need mounting hardware. Take note that the front screw is longer then the two rear screws.
Here is the thread link. Should help!