Modine no longer lists a radiator for any AMC car older than 1980 in their catalogs (the one they list is 1R-579) and they had nothing in the cross reference for your part number. You may be able to find something that will fit. The catalog can be downloaded from http://www.modine.com and has dimensions in it.
I looked all over their site, I find nothing but corporate mumbo jumbo; couldn't find a catalog, but I found this:
As of July 22, 2005, Modine Manufacturing Company no longer operates business in the automotive aftermarket segment. This is due to the merger between Modine\u2019s Aftermarket Division and Transpro, Inc., which combined to form Proliance International, Inc. (AMEX: PLI). Modine shareholders will control 52% of all Proliance shares as of this date.
I guess I'll do my usual, adapt some common part to the job at hand and stop trying to push rope.
Thanks Joe for the lead; I'll call Midway tomorrow and see what they say.