Both the crank and waterpump pulley on all Pantera engines are special- that is, different than that put on Mustang 351Cs. The pulley diameters are smaller, the pulley ratios are different and the pulleys themselves are cast or forged iron rather than stamped steel. There are balencing holes drilled in each. I know of no other application- a Mustang crank pulley will contact the main water hoses, probably sawing thru them in short order, and will affect the speed of water flow through the radiator. To my knowlege, there is zero difference between the '71 and all other year Pantera 351C pulleys.