Ford only made the Boss 351 in 71, if the motor in your car is not orginal there are a few ways to tell if it is a Boss. The Boss 351's had aluminum intake manifolds, dual vaccum advance on the distributor, dome top pistons, and beefier connecting rods. I think the Boss motors were the only ones to use a square carb mounting flange the rest used a spread bore design. Ford also used 4-bolt main blocks on the 351CJ during these years so you could have one of those.
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