You've either found a 53, or 71 series, and each came factory in trucks.
If by some chance you found a 4-51 (doubt it though, would have said GM diesel) they too came in some trucks but not many and perhaps not in this country.

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-