Your Transmission cooler lines should be plumbed to there , it was probably leaking , so it was bypassed and you should have a external oil cooler in front of the radiator someplace . You have a couple of choices at this point , have a radiator shop rebuild your current core if possible , find a NOS radiator or get a new china built aluminum crap replacement radiator . Bear in mind the NEW replacement radiators are not QUITE the same as the original .Do a search and you should be able to come with lots of info on the subject of replacement radiators for your ride .