Fe take some precausions to keep them from leaking. The rear where the intake manifold and block and heads. If you have milled much, the manifold fits so close to block the original cork gasket going from head to head accross the block will not fit .
Oil resistant RTV works as a substitute. fill the corners . Do not cut the exscess intake manifold gasket material sticking up along the valve cover rail. If milling was right head and intake rails should be close to the same height. After torque intake manifold , lightly and carefully peen exscess intake manifold gasket material down to the valve cover rail with the bulk of the material going toward the lower area ,rather it be manifold or head.
Oil resistant RTV again any gaps. I used
oil restant RTV for valve cover gasket. Apply bead to clean valve cover . building a smooth 1/4" layer . Let the RTV dry enough to form a good skin. Wipe a coat of oil onto the sealing surface of the head and intake manifold with your finger and the bolt the valvre cover loosly into place( slight pressure). wait tilll the RTV has set up to tighten much. result is it doesn't leak and gasket is reusable. Who said all fe's leak? I used to wiz most of my money as a young man in 69through 75 on FE engines.