Hey there and welcome back!
Glad to hear you have got your title sorted out and can continue on with trying to ID what you have! With that in mind, I think this
1955 GMC Truck New Model and Features document will go a long way in helping ID your basic truck details. I had to read through the entire thing to try and pick out the pieces that help define your truck.
Clearly it is a "410" series which coincides with the 1st and 2nd digits of your serial number. From what I can tell from the booklet, the "410" series came in 4 different wheelbase option lengths, indicated by the numbers 1, 2, 3 and 4. Using a best guess thought proccess, I think the 3rd digit of your serial number would indicate the #4 wheelbase. The "Y" character denotes the "1955" model year. That leaves the last 4 digits "1550" to be the sequential production number as that truck came off the assembly line. I don't know for sure on GMC, but Chevrolet production numbers usually started with the number 1001. If GMC is the same, then your 1550 serial number would indicate it was the 550th truck off the assembly line for the 1955 model year.
As I said, this is just what I can figure from reading the reference document and more on GMC Serial Numbers from
this Serial Number Info Page from Old GMC Trucks. I think some of our fellow GMC owners with more knowledge than I have will come along and correct any of this info I may have guessed wrong on, or maybe add more details like what the "#4 wheelbase" length actually is.
Hope you enjoy reading the resource document and this info may help you move on to more steps in your project!
