53 series Detroit didn't come out until 1958, same time the V71 engines were introduced. Neither 318 cubic inch 6V53 diesel or the 318HP 8V71 diesel would be original engine in a 48-50 truck, or anything prior to 1958 or 59.
What year is the truck exactly?

That's a mighty nice looking truck, I'd sure like to see more of it!

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-