Bob,
I am just basing my thoughts on my observations on known original jacks and information from the mid-year Corvette guys. The same company (AUSCO) made those jacks, and there is supposedly some detailed documentation that has been obtained about the Corvette jacks. I'm currently working on trying to find out exactly what information is available. I just know that the Corvette guys have it nailed down for those cars. Obviously that is often times easier to do for the Corvettes due to the limited production, and the fact that all of those cars were built in the same plant.
Like Marcus mentions, I have found that this is the first Mustang version, but I honestly have a lot more to learn about these jacks. I have found it very difficult to verify if particular jacks originally came in certain cars. Jacks are obviously just something that get swapped out quite often among cars.
It would be great if we could obtain real documentation from the original manufacturer.
Marcus-I am very interested in learning about your findings. When do you think you will have your observations available? If you have bits and pieces of information available for the 64 1/2-66 Mustangs, you can send me a PM with a general outline if you have a chance.
Thanks to everyone for their input, and I will look forward to learning more.