Although they are all the same 71-74 Pantera's there are differences chassis to chassis. Most folks who 'need' these may be looking for that adjustability in caster, camber and toe that the spacers would offer. As David has stated the vendors usually adapt off the shelf parts to Pantera application to keep pricing acceptable to the masses and so they can spread their design cost an still make a buck. One off solutions are available if you bring your check book.
Larry Stock must have changed his design as the adjustable a-arms I have are adjustable on the outboard side using a heim (rod end) instead of the ball joint. Are those bushed ends? Are they double sleeved to be adjustable on the car without removal?