Welcome to the Forums!
Do you still have access to the seller (and are they local to you)? If so, they would be the absolute best person to do this walk through. The challenge with a restored or customized unit is that it might not have been set up to be "standard," so even someone who is familiar with the way trailers were set up in
1966 will be lost when he looks at your trailer, which has had modifications/modernizations done to it.
Another option would be to look at the Portal tab of these forums, and scroll down, keeping your eyes to the right of the screen. There is a utility that helps find Forums members who are volunteer trailer inspectors. One of these folks might be able to help.
good luck!