I possess a Sears-Ted Williams Model 75, 20 gauge shotgun wi...

I possess a Sears-Ted Williams Model 75, 20 gauge shotgun with a switch at the end of the fore end with a lever to select H and L, in addition to an adgustable componant at the end of the barrel marked Full or Mod or Imp Cyl. What is the purpose of these adjustable componants? What would be the value of this weapon in good condition? Otis James

The lever on the front of the fore end allows you to select "high" or "low" brass shells meaning high power hunting ammunition or low power target shells. This lever adjusts the amount of gas which will be directed to the piston which cycles the action, ejecting the spent hull and loading a fresh shell.
The adjustment at the end of the barrel changes the amount of choke (or restriction) of the barrel which will concentrate the shot pattern for longer ranges. "Full" choke is tighter than "Improved Cylinder".