[bobcowan]

I would leave your brass radiater in place for now and see how it goes.

The small outlet is not that big of a deal. You'll need an adapter to increase the size for the BB. But that's not a big deal, either.

A good fan with a shroud is a must have item. Doesn't have to be anything fancy/expensive, but don't cheap out either. The fan needs to fit the opening fairly close. And the shroud need to encompass the entire core, and fit closely. I'm using a 16" spall fan adapeted to a stock Mustang shroud with good results.