I had the same problem when I up-dated my engine from a 1950 235 cu.in to a 1961 Cu.in. using the 1950 intake/exhaust manifolds.
After dressing all the surface areas, and putting the manifolds back together, I just couldn`t get a proper seal. Finally I loosened the bolts and nuts which hold the exhaust to the intake manifold, re-alligned the manifolds to the block, tightened all the manifold bolts, and lastly, re- tightened the intake to exhaust manifold bolts. (solved the problem).
