Swampdog is correct the lever on the left front is the Magazine Cut-off Lever. Meaning it is basically in single shot mode when this level is flipped back to the rear, eventhough yo may have a mag tube full of rounds.

As for the correct sequence or order of the bronze & steel washers on top of the the recoil spring, there is usually a diagram showing the correct order for heavy and light loads pasted inside the forearm. Being that it is a 16ga and not a 12ga 3" mag, there should only be one each of those " Bronze Friction Piece" inside the " Friction Spring" and a " Friction Ring" at the base of the " Recoil Spring" . If I am not mistaken the only adjustments neccesary are:

HEAVY LOADS:
Take the " Friction Ring" from the base or bottom of the " Recoil Spring" and move it to the top of the " Recoil Spring" with the BEVEL facing forward toward muzzle and then place the " Bronze Friction Piece & Friction Spring" against the BEVEL of the " Friction Ring" . Re-assemble the farearm.

LIGHT LOADS:
Take the " Friction Ring" and place it behind or at the bottom of the " Recoil Spring" against the receiver with the BEVEL facing or against the receiver. Re-place your " Recoil Spring" , the your " Bronze Friction Piece & Friction Spring" . Then re-assemble your forearm.