Gene:
Look at this thread I found on this board:
http://forums.performanceyears.com/g...811#2576029811
Apparently the difference is in the heighth of the radiator that the core support will, well, support. Frost what Marv says on this thread, all 64 GTO's and the Lemans's that had A/C all used the same core support. The rounded core support apparently was used on the Tempest and Lemans cars that didn't have A/C.