I have a 4-53T silver in my 48 2 ton, requires firewall modifications among lots of other things.

Have seen a 6V53N in a similar truck, guy did a very nice job and didn't have to cut firewall. However it was stuffed in there real tight, not something I'd want to work on and maintain ongoing. Having seen it a few years in a row I don't think he puts very many miles on it.
It is also a whole lot of weight compared to the original gas engine.

•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-