I know of four. Three are round gauges. There is the early model that has chome on the edges of the gauge wells AND the wells, then there is the mid models that had just Chrome on the edges of the wells. Last there is the sport and cruising wagon models that had the flat faced cluster with the tach.

Then there is the 79 to 80 models that used square gauges without the round gauge wells.

I know that at least up up 73 the white gauge plastic assembly is different due to a smaller connector and less bulbs used, and the speedometer up to 110 mph.

I know that up to 78 they use more illuminqtion bulbs and speedometers only up to 85 mph, also a wider connector.

Sport and cruising wagon clusters use a different flexible circuit board to incorporate the tach.

Not sure if 79 to 80 can be swapped with the 85 mph round gauges, but i dont see why not unless there were wiring changes.

74 -76 also went up to 100mph before they changed to 85 in 77. Although Cookieboys 78 hatchback has a speedo that goes up to 100mph & as far as he knows it has never been replaced.