Changed the intake manifold, now there's an exhaust leak between manifolds.

Your problems here are:

• Not a good choice of gaskets, especially at the intake-exhaust junction. That stamped-metal gasket often won't seal worth a crap with used manifolds, and stacking two of them is a surefire recipe for major leakage here.

• Very improper manifold installation procedure. You can't just tighten whatever bolts in whatever order to whatever torque and expect things to go well.

Take the manifolds off — all the way off — and start over again. First, do what is necessary to ensure access to that inboard intake-exhaust stud/nut. You may have to drill, slot, or enlarge holes in the carb adapter plate. The nut needs to bear (via an appropriate flat washer) on the intake manifold surface, not on the adapter plate.

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Follow the install procedure and torque specs described here, except the Remflex gaskets call for less-than-factory torque on the manifold-to-head nuts, so follow that spec.