We're almost done putting a new motor into a 1993 Suburban with a 350, and last Friday we were going to put the manifolds on and the bolt holes weren't lining up. So today since we finally had the time, we took them up to an auto parts store/machine shop and they have an "Exhaust Manifold Spreader for Smallblock Chevrolet's." Both of my grandpa's, my great uncle, two uncles, and my dad have been working on Mopar and some Ford for all their lives and have never had a manifold warp so the holes don't line up. The guys up at the shop said that it's a common thing with chevy manifolds. Any idea why these do this? I understand expansion and contraction of metal but when the manifolds were taken off they were cold and it hadn't been run in a couple months.