Front Wheel Vibration

Something's definitely not right up there. I assume you had the wheels & tires spin-balenced before mounting, correct? If not, be aware that all tires and most wheels have 'heavy spots' that will pulsate, especially around 55-65 mph. Other things that contribute may be- a bad steering rack bushing, an incorrectly fastened front wheel axle nut (std '71-73 Pantera front spindle nuts are not re-useable unless the front spindles are drilled for conventional nuts). There are too many possiblities to guess at- I'd take this to a front-end specialist for a thorough look-over.