Is a GMC truck just a dressed up Chevy truck?

pt70 said

The early hemis were in dodges, desotos and chryslers. They were totally different motors.
Ford and mercury had similar flathead motors. Mercuries had a few more cubes and horsepower.
Some early GMC trucks had pontiac motors in them [straight 6 cyl. flathead with 2 cyl. heads.]
Up to the mid 1970's all gm products had different V-8 motors. Buick, olds., pontiac, chevy, and cadillac were all different. Mercury had a 410 which was an overgrown 390 ford. Lincoln had its own flathead and its own 462 V-8. There was a lot of stuff happening back then.

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When I got out of the Navy in 74, I was working in a parts store. A local kid had a brand new Firebird, with a Chev engine. He had come in looking for an air filter, and this was the days when a big huge note in the catalogs told you to get the code out of the VIN. I asked him if he knew whether it was a Ponch or Chev engine and He told me "Pontiac" and I did not double check. Came back later, "it won't fit," went out and opened the hood, I took one look and announced, "Chev." He says "How can you tell?" and said "I thought you were kidding." There were lots of crestfallen / surprised looks back then