I have a big Griffin radiator in the cuda. Bolted right in and works great, but it was expensive. It's a down flow w/ two rows of 1.25" tubes. The Champion radiators that a guy sells in the classifieds here on the board I hear work good, and they're cheap too.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax