We replaced a Griffin with a Champion in my brother's 78 Z28. The Griffin had about 4,000 pampered miles on it and started leaking. The Champion is lifetime warranty. The two row G body unit is rated for 525 HP so I think it should suit your needs fine. Down here running A/C in the summer, I would probably go with the three row which is rated for 750 HP.
Oh, the Champion radiator fit my brother's car much better than the Griffin. It sat right in the saddles without modification. With the Griffin, we had to carve out the saddles to get the tanks to sit in them. I don't like that the Champion is made overseas but I do like that they stand behind their product. Also, if you want to pay more, they will make you one here.