Re: 258 exhaust manifolds
I'm 90% sure you're stuck with the pre-80 manifolds. The older ones have the flange for the header pipe centered in the manifold, facing straight down, while the newer ones have thye flange more toward the rear of the block, and I think angled slightly toward the rear also.
In addition to the o2 sensor bung, there is the egr pipe that runs back up to the intake manifold on the 80+ models.
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