I'd think they'd fit between the frame even up front where it tapers. I have a 4-53 Detroit in stock location in my 6400, same room between frame as the COE and it's not a narrow engine.

I find it hard to judge engine and frame fit with just drawings because both are complex shapes that actually fit better in and around each other than overall dimensions would suggest.
No substitute for a trial fit.

•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-