I understand that they were found more in larger trucks. It is amazing how many people have not heard of or seen them. I hope you got all of the pieces to install them.
I saw a set in a 55 1st series truck sometime in the 80s. I talked with the truck's owner about them and years later, bought an extra set from him that he had picked up.They had been in storage waiting for me to get to that part of the project. I ran across another truck owner and member of this site that was mostly done with a beautiful 55 1st series truck. He was determined to install all possible options but had not heard of the seats. After searching for a set for him to restore and coming up empty, I offered the set that I had with the understanding that he would replace them to me in due time in similar condition to what I sent him. This bought some searching time as I am not setting any land speed records getting my truck done. He sent me pictures after he had restored the truck with the seats and they looked amazing. I helped to try and locate a replacement set. It seemed to be pretty hit and miss. Then 2 big boxes showed up and when I opened them, they contained the seats you see in my pictures. He had decides to reward my "leap of faith in sending them to a complete stranger" along with a very nice letter of which I am equally proud of.
When you get ready to install your seats in your truck, check out the other albums in my webshots and feel free to ask questions.