Had a few of the single players over the years. Very bright & colorful play fields which last very well. Some nice themes and well designed games. Some weird ones as well. Some decent cabinet art, which was unusual on EM pins, Very popular over here in the UK, at the time. Basically the EM games are Williams inside, all the coils, steppers, score units, relays, score motor, most things are Williams. The first couple of games actually had Williams on the apron, changing to the triple Z apron a bit later. The three Z's were for the three Zaccaria brothers, who owned the company. The pops are the same design as late Gottlieb EM which will fit, though the art differs on the Z capped ones, others have designs that are close enough to allow Gottlieb ones to be substituted, unless it has to be totally original. Early games had a chime box which was the same design as a Gottlieb one. The electronic sound cards on later games, which also make the Biri Biri at 4 million, are very difficult to find. The one on Combat has an extra board to produce the explosions as the game is played. The later games also had an electronic card to make the pop bumpers and some other lighting flash, to give higher scores.There is a lot of info' on www.zaccariapinball.com, including many schematics, plastic scans and wiring diagrams for the sound card.
Some of the art was by Lorenzo Rimondini and he signed some back glasses, on the tail of Concorde on the Supersonic back glass, for example. It was common for two different back glasses to be used during production. I know there were two versions of Supersonic and Moon Shot, and probably others.
All in all, they're not at all bad games to own and play. As well built as US games, with better play field protection, better clear coat is the reason for that.