they would be 3-71 Detroit diesel's
your choice of the two stroke series (displacement per cylinder) are
51, old and hard to find
53
71
92, only made in v type
110, only made in an inline 6
149, only made in V type

•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-