hello, i don't think that anyone modified the brackets but i think the place that got your radiator got the wrong one as there are a few different ones for your navigator. here is a list of the ones available.
I know that generally there can be two different size (core) radiators for the 2003 Navigator. What I need to KNOW is what are the physical dimensions for the 1" core for my car supposed to be. The search I did for my VIN said a 1" core. Do you want to search the VIN and give me the actual dimensions for the radiator that's supposed to fit? If so, it's:5LMFU27R33LJ45995