Here is the alignment documentation from my 1967 Midway Space Gun. I imagine they are very similar (just different targets).
Also, when I got my game I noticed a wadded-up ball of bubble wrap wedged on top of the wiper board (the bakelite board that holds the contacts). Turns out that the bakelite board was warped and the previous owner did this to 'flatten' the board and make it score accurately. I found this out the hard way by removing them and throwing the aim off wildly. In fact the board was so bowed that the stylus arm from the gun would not make contact in many areas. If you see this issue on your game, check to see if that could be the problem.