I think finding a used aftermarket or original radiator (and separate trans cooler) for your truck will be a better option than finding a used but doesn't quite fit right radiator from something completely different.

But even then you may find you're better off with a new one, then you have a better chance of getting a serviceable one to start with. Could be that a used one and a new core is less cost effective than a new one?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-