It is NOT for a pre-63 GM 6-cylinder.If it fits GM, it will be 63 and up when they made the 194-230-250 and 292.I would almost guess it to be a marine manifold,,,,,or off an engine from a generator (large type). Are you positive it is GM ??
There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us. - - Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!
