Just a thought, it's kind of a shot in the dark but have you checked to see if the radiator can/will mount on the other side of the flange it bolts to? That is assuming it normally bolts to the engine side of the flange. Also I think I'd be having a conversation with the outfit I bought the new radiator from. If they are selling them as a drop in replacement and they don't fit there is a problem that needs addressed.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.