[ChevLoRay]

Until 1960 and the change in body styles, GMC used bigger straight-6's (261 and 302), than Chevy (235 and 261), but they also used Pontiac and Buick engines. I had a '38 GMC half-ton that used a Pontiac 226-cid flathead six. Larger styles used larger engines. My '58 Chevy truck shop manual also referred to other engines that were used, including Buick V-8's and Pontiac V-8's. These were in addition to the diesels that were offered and used. The '55-second series and '56 GMC had as an option, Pontiacs' 287 V-8, then followed up with the 347 in '57.

I guess that was the lure that GMC had, the availability of larger engines in the same body, plus a slight change in styling.