Disc Brake Master Cylinders?

All three of the master cylinders pictured have larger rear reservoirs than the front. The rear reservoir on the one on the far left is marginally larger but is still larger than the front. All three are definitely about the same depth size and not as deep as the 73-up disc master cylinders. Are they in fact for disc brakes? Based on the covers anyone have an idea of what vehicle/year they are for? Comments welcomed.