Pretty much it needs to be the factory size radiator. I believe between the mounting studs of the magnum powers IC its about 20" so rad needs to be less than 19.5" and tall about 19" as well, little more flexibility in the height, but not much.
Down flow preferred. Brackets will need to be welded to hang it on the mpfmic, and that's on the side.
Worse case scenario. It will have to be the $500 griffin but trying to avoid that.