What do the model numbers on Bastion's body represent?
There is no official lore for what the numbers mean but I would presume they are version, unit or batch numbers. I doubt they reference a specific kind of Omnic robot as Bastion is the type, not his name as might be thought.
From Overwatch's website character lore
Originally created for peacekeeping purposes, Bastion robot units possessed the unique ability to rapidly reconfigure themselves into an assault-cannon mode.
(Emphasis added)