Ideas:
1. Are you running any fan spacer? With the wimpy "194" style damper you dont need any which gains some clearance - I am running a bigger "250 truck damper" and had to space the 4-blade fan out a bit to clear it
2. I checked a 4-row crossflow rad once in the Chevy II, same problem the '6' is too long.
3. A stock 2-row v8 rad has a lot more area but is no thicker, drill new holes and it will fit.
4. Rather than ditch the nice new alum rad, what about getting an electric fan?