Interesting find.

Apparently, Canadian 261 Pontiac engines have the 848 heads. Reference: https://118110.activeboard.com/t60840366/261-canadian-pontiac-with-848-heads/

I'm guessing that the stamped serial numbers are a different format from the US format. (digits only)


This thread should be of interest to you:
https://www.stovebolt.com/ubbthread...ontiac-261-vs-truck-261.html#Post1028317

Gord 🇨🇦
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1954 1/2 ton 235 4 speed