Maybe this will help explain it.
http://oldcarmanualproject.com/manuals/GMC/1979/LTService/06E/pages/79GMCService0701_jpg.htm

Get the numbers/letters stamped into the block behind the distributor and post them here. It may help ID your engine.

Oh. I see we already tried that: https://www.stovebolt.com/ubbthread...ing-which-engine-i-have.html#Post1402666

Last edited by Gord&Fran; 01/03/2023 5:02 AM.

Gord 🇨🇦
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1954 1/2 ton 235 4 speed