Follow up on Tim's question first.

But the simplest "bolt in" swap and the most bang for the buck in my opinion will be a 261. They are "more modern" than what your truck originally came with, but not a "modern" engine.

a close second choice would be a 235 with full oil pressure, likely you'll find you already have one.

Either engine can be adapted to full flow oil filtration (if not already) and use a spin on oil filter if you desire.

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-