The manufacturer produced the backglasses in both crystal glass and Plexiglas. Near the center of the motor board is a 10-pin jack with a 4-pin shorting plug. This shorting plug is required for replay operation. This jack will accommodate an Add-a-ball relay, likely ordered separately by the operator, required for Add-a-ball operation. The operator would remove (and save) the shorting plug and attach the Add-a-ball relay to the nearby vacant area of the motor board, plugging it into the vacated jack. In the Files section are instructions for converting this game from Replay operation to Add-a-ball operation. The schematic refers to the "add-a-ball relay". Early Production games (like the ones featured in the promo photo and the flyer) differ from the rest of the production run because they have no "Special" on reaching letter 'E' of 'Rocket' on the playfield, thus no Special light on the left outlane, and no left outlane kickback. Also, they feature a bottom arch with different graphics, different colors on the playfield and the cabinet (while the plastics are the same), and a different playfield glass, being the familiar sliding glass, while later in production the glass was changed to lift upwards from the front in a metal frame. Although the games featured in the flyer and in the promo photo are normal replay games, Federico Croci, a collector in Italy, tells us that several Early Production versions were found there with no replay unit and no replay window in the backglass. The Italian add-a-ball version is Bally's 1967 'Rocket III (Italy)'.