Shred, It actually helps cooling because it puts more surface area across the airstream in a given dimension. The fan choice plays a HUGE roll. The H1 Humvee has the radiator mounted on top of the engine. It's pretty weird but it works great. In that case they have a major fan working on it.
I'm hoping I'll have enough room to just go standard location. Slanting the radiator is a lot of fabrication work. I like your solution, Tom: With the cap located somewhere else. Ford did this for the Cobra 427s. They had a separate expantion tank with a cap. It's something to think about.