The Napco emblem shown is now sold as 57-59. Those were the "factory years". This indicates that the Napco kit may not have come with an emblem in pre 57 kits or that it was only on factory units. I Don't think the name "Powr Pack" was used until TF trucks. The 3600 emblem is 53-54 as said. The first J in the serial is from a different stamp set. The reason the installs were all the same is they followed the instructions.
Plenty of units could have been self installed to save money. Many in those days were purchased by utility companies, government, oil, gas exploration, miners, loggers. They would have had their own maintenance shops.
Other buyers were farmers and ranchers. They were better equipped and they were better mechanics than anyone else. Part of the advertising was "Easy to Install and can be transferred from truck to truck" 4 holes to drill.
Very few were bought by a hunter or a city slicker. You had to have a real need to spend the money....or be wealthy. I have never owned one that the original color was not what I call "Forest Service/AG Dept Green".
