In doing my research for madeulook, both Jim and Bob in Wisconsin told me they were big block Galaxie radiators, lowered about 1-1/2". Bob had an NOS Big Block radiator in the original box. Re-coring that was a sign of faith IMHO! (and expensive)
The small block radiators were never wide enough to fit what the race team did to the radiator support panel. All the real deal R's I measured had small differences in the radiator support openings.
So, now knowing what I learned, the trick would be to gather 428
Galaxie radiator top and bottom tanks, and head to your favorite radiator shop. The side frames are a lot easier to locate and can be soldered on at home.