I had the same issue with a 270 manifold. Try heating the intake manifold just barely red hot with the gas wrench in the vicinity of the bolt holes. It worked out OK for me with no breakage. Good luck!
1946 Chevy pickup, 1948 Chevy suburban, 1950 Chevy pickup, 1952 GMC pickup, 1957 Chevy pickup, 1939 Chevy pickup
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