Did all the Flange Holes line up with your Radiator Support? If so, I would just say that it is a poor quality replacement. I'm not familiar with that brand. I would be calling them though, just to see what they say about it.
Another reason I like sticking with repairing/rebuilding/re-coring originals. Some of those replacements don't look correct as well.
That said, I bought a replacement Radiator for my '72 C-10 Truck. It was very original looking, so I brought it home and it fit perfect. I would had return it if it didn't.
Keep us posted on it.
-Parting Out over 75 '58 to '73 Full Size Chevy Cars-
-National Impala Association
-Vintage Chevrolet Club of America