Depending on the rest of the package(cam, intake, exhaust)you may see a little gain assuming your 69 heads have 2.11/1.77 valves. May end up pinging as well. I know my 400's with 72cc heads will rattle even at my 4500 foot elevation. Going to be worse at sea level.
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Jack Ferris
RestoRacing LLC
www.restoracing.com
Sandy, UT
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