We just did my sons 326 a couple years ago. We had the 250 hp and made these changes. Bored it .030" over. Replaced the cam with a Crane max Velocity hyd cam #283941 Replaced the 4 sp with a TH 400 used an Edlebrock rpm manifold and a 600cfm Edlebrock carb. We went from a 3.23 axel ratio to a 3.90 posi and instralled Hooker supercomp headers through 2 1/2" pipe back to the rear axels, and the thing runs great. Just a little lump at idle of about 700 rpm and good response with the 3.90 gears. Headers help, but, if I did it again I would get the factory HO manifolds. These headers fit good but as with all headers they are a pain in the a##
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