Here's what some of those numbers mean:

From the model number, 255 means it is a first version 1550. (There was no 155, as all the other models were already up to 2 when the 1550 came out, so they started there.)

21287 goes like this, 2= adjustable wide front, 1=gasoline engine, and 287= I' don't know yet, but it has to do with options on the tractor.

the 504 after your serial number is your transmission code, which is the regular speed row crop transmission. 502 was the code for the high speed version.

If you want even more information about that tractor, you can order a copy of the build card from the Floyd County Museum by calling them at 641-228-1099. The build card tells what day it was built, shipped, as well as what options that tractor had when it was built.