I was thinking about this because of what I went through to put a GBODY TII radiator/intercooler in my 90 Shadow.
That radiator didn't fit because of the filler neck. My friend at the radiator shop relocated the filler neck down a few inches. Then he brazed a plug where the filler neck use to be. Even then, we had to cut the hood bracing to clear the lower filler neck.
The same radiator is in my 91 Shadow. The 91+ cars have a different core support. The radiator fit in just fine, but is a bit taller then core support.
This got me thinking about one radiator to fit all cars. Was the filler neck relocated to account for the varying differences of each body car?