I recall quite a while ago (just remembered this now...guess old age catching up with me) that Pontiac didn't actually use 4-core radiators on Firebirds. I just checked the assembly manual, and that seems to be correct. The 3-core was the largest.
The 3-core was used on 350 cars with HD cooling specified, and all a/c cars. Same radiator was used on 400 HO and Ram Air cars, and 400 cars with HD cooling. There was a 'Super Cooling Radiator' option, used on full sized Pontiacs only.
I seem to recall a discussion on another forum about a 1969 Trans Am RAIV 4-speed, and there was doubt it came with a 3-core radiator, but apparently it did. Ditto for another example where a fully loaded Firebird 400 w/ac had a 3-core HD radiator.
