A little history on the 400 BB. The 396 debuted in mid 1965, and was run
through the 1969 model year. In 1970, it was still billed as a 396, but was
actually bored .030 bigger at the factory to 402. In 1971, it was sold as a
400, which was the cause of much confusion because of the 400 sb that also
came out in 1970. An easy way to identify it is the balancer. A 454 in
externally balanced, and the balancer is not evenly weighted all the way
around, where as the short-stroke 396/402/427 all used the same crank and
balancer. It is smooth and evenly weighted. In a vehicle as old as this 1972
is, it's quite possible that the original 402 was replaced with a 454 due to
the fact they are easier to come by than the 402 is these days.
Devin
big block guru
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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