Sometimes intakes will bolt right up correctly and sometimes they don't. Before bolting up a 'new to you' big block manifold, set the intake on the heads with no gaskets and check that the intake surface is parallel with the head surface. If not, mill the intake appropriately until it is. Then note the alignment of the bolt holes and the ports and use gasket thickness combinations to give you the proper fitment. Try to be smarter than your intake manifold.
