I understand that the 90's era radiators have a straight input, not angled upward, and that change might have started in 1972, meaning a 1967 radiator input flange is angled upward 30 degrees and a later model the input flange comes straight out of the radiator.
Like this example, I think this is the later model radiator:
Here is a radiator similar to mine on the lower input, angled up. (THIS IS NOT MY ACTUAL TRUCK)
