Some people prep the new manifold by enlarging all the mounting holes in the manifold a bit (except for the center ones. They have to be left 'as is' to locate the manifold.) Enlarging the mounting holes allows the manifold to expand a bit with less stress, as it can supposedly 'float' a bit on the expanded mounting holes. Probably helps the studs last longer too..?
in addition, check that the mounting surface of the new manifold is flat, as it may have twisted since manufacture. Resurfacing a manifold *after* it has been in use for a few years and heat cycles should ensure that it's not going to twist any more.. Also, there's the advice to make sure the motor mounts are in good shape, so the motor isn't hanging down a bit, and stressing the manifold on the exhaust..
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