Like Techinspector says, you need to check and confirm the numbers. I've seen folks do some pretty "shady" things with Chevy small blocks, since from the outside, and without checking the numbers, you would be hard pressed to tell one from the other; there are some subtle distinctions, but unless you are a hardcore "Mouse Motor Freak", they would likely not be recognizable to you. If your truck is an original, unmolested one, again, hard to tell just by a casual look, that engine should be a 350 or a 400. I have owned a number of K20/K30 Chevys from 1978 to 1982, and they all had 400 CuIn. engines.

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