Most modern `donor` rads tend to be of the wide cross flow design Jay, so possibly not much choice there for a "hi-heat output" blown Chevy mounted behind a tall skinny Pop grill shell!, but there should be a few suggestions along soon!.
Our own "Pop Brown" (Kris Brown) here in the UK sells aluminium radiators for Pops/Anglias, including a heavy duty `Big block` version, which has proven popular (no pun intended ) over the years!. Chris is very helpful and been a UK rodder since the `60s.
http://www.popbrowns.co.uk/products3.html#ALLOYRADIATOR
I would think that any of the big US rodding radiator suppliers (Walkers, Brassworks, Griffin etc) should possibly be able to supply one to fit within the Pop`s slim grill shell too...
http://www.walkerradiatorworks.com/
http://www.thebrassworks.net/
http://www.griffinrad.com/exact_fit.cfm
http://www.prchotrod.com/products/pr...-radiators.php