Both of my machines have had cards saying "see attendant for jackpot" placed in front of the jackpot hopper, behind the glass. Both machines also have a spring that's landed to a loop on the baseplate casting, but not connected to anything. Both machines also have, just to the left of the jackpot slider, a shaft that has a cotter pin hole in it that's presumably for another slider or lever that I don't have.
Here's a picture of the location in question.
I'm thinking that the missing pieces are related to some function of the jackpot payout mechanism?