J.J.
I can't answer your question, but suggest you call Power Trac and ask them again. Sometimes they don't route the question to the person who knows the answer. I think the man other than the boss who knows the most may be Don - in charge of parts. Kristie Asbury, in marketing, is a daughter of Ed Reynolds, who started the Company and is still the boss. Kristie may not know all of the history, but can ask her father.
On one of my visits, they showed me the original PT. The company had been in the mining equipment business when Mr. Reynolds became dissatisfied with the machine(s) he had to care for his place. I was told that he designed and had his shop build the articulated machine which they are preparing to display as the first Power Trac. It had a lot of the characteristics of the current 400 series machines. If you call, they should be able to give you the date of that one, and I am sure Ed Reynolds can give you a complete history if you can get through to him.
Terry Estep has always been helpful on maintenance and repair issues, and may know about history, as well. He also may be a conduit to Ed. Reynolds.
Let us know what you find out.