In response to the competition from quartz watches Bulova developed the 219 calibre. Citizen had made Hisonics which had movements identical to 218s. However instead of just using the 219 movement they developed their own cost cutting calibre, the GX Cosmotron. This has many similarities to the 219 but there are some important differences. The tuning fork has the counter weight on the opposite side to a 219 fork. The coil assembly is a modified 218G in which the drive coil resistance is 11k ohms. Like a 218, the coil can not be removed without dismantling the train and loosening the fork. Unlike the 219, 218 index wheels with capped jewels are used. The name is interesting because Cosmotrons were electrically driven escapement watches with nothing in common with the GX Cosmotron.
The examples in the box are all fully restored. About half the models have the movement inserted into the case from the front. The back and the bezel are both clipped on and can be incredibly difficult to get apart. The ones with back inserted movements have a very fragile plastic movement ring which is sometime found to be broken or missing. When missing the movement can sag down and allow the top of the fork to touch the back. However I think the positives outweigh the negatives.
Photos show GX and 219 forks, GX coil and 219 circuit board.
The box is Grevillia robusta or Southern Silky Oak, from an Australian tree grown in New Zealand.