Chryslers in 70 and 71 had a track pack and super track pack. The track pack was a dana rear with a 3.54 rear gear, and some other stuff. The supertrack pack was a 4.10 dana on man and autos and had power disk brakes, stiffer leaf springs biased towards the right rear, and a few other things. It was all stuff made to take the power and abuse of a drag strip. I'm sure that's what the mach 1's that have that decal have had done to them. Probably a rear gear, different springs, etc. But who knows? Ask one of the owners.