I finally picked up a flash suppressor with the bayonet lug for my m1a while I was getting some other parts from Fulton Armory. Eventually I'd like to fill in the hole in my wood stock. I see there's two options for the replica f/a pieces which would fill in the wood. What's the difference between the button and switch? I assume one was an early adaptation and the other came about later? What would have been correct for Vietnam era?