My 2 cents: serial numbers are probably the least important aspect in a dio such as this, unless you have good solid reference. I do know that for the US Army in WWII, the first two digits of the serial number denotes vehicle type. The rest was vehicles individual number. Also that a “S” suffix on the serial number denoted that the vehicle was equipped with a radio suppression system. I remember having those on tracks that I crewed upon long ago, but no longer recall their exact function.
Bumper codes are more important if visible. After all, you would not want to use unit bumper codes for an Ardennes diorama for a unit that did not serve in the Ardennes, say the 1st Armored, or 1st Cavalry Divisions, they served in other theaters. And even if you go with a unit that served in that battle, at least use one that served in the proper area. You would not want to use bumper codes from units that served on the northern flank of the Bulge, when your diorama is set on the southern flank. So a little more research to see what sort of units did route control in that area will go a long way to telling you what you need. The individual vehicles bumper number, without a good photo reference, will be an educated guess at best, based upon standard army regs and practices.
actually that was about 5 cents...