If the manifolds did not leak prior to removal, there is no need to have them machined. If you separate the intake from the exhaust manifold, make sure to leave the fasteners loose which hold them together at the heat box while you tighten the manifold assembly to the head. Once the the manifold assembly is torqued to the head, you can then tighten the fasteners which hold the intake to the exhaust manifold.
A tip to loosen up any of the bolts without breaking them is to actually tighten them slightly until some movement is felt, or a sound is heard. Don't ask why it works. It may well be magic.
Carl.
