When I removed the cat from my '81 I only added a test pipe where the cat was located. The next step was to disconnect the belt and then the removal of the smog pump because it is nothing more than an eyesore and hides the nice valve-covers. Part of the removal of the pump was also the elimination of copper plumbing that led from the exhaust manifolds. When I disconnected the pipes from the exhaust manifolds, I found some nice brass caps that screwed right on and sealed the manifolds.
One more thing... here's the description of the Air Management System from the '81 shop manual (page 6E1-5)...
The Belt driven air pump, AIR, is controlled by signals from the ECM and vacuum.During cold operation, air flows to the exhaust ports to help control HC and CO and help warm the engine and catalytic converter more quickly. During deceleration and wide open throttle oprtation, air is directed to the air cleaner to avoid excessive noise. Excessive air pump pressure is also directed to the air cleaner. After the engine is warmed up, air is directed to the lower bed of the catalytic converter to provide an oxidizing atmospherre for effective catalyst operation.
The air management system has an electric air management valve or valves that divert air to the sir cleaner or switches air between the catalytic converter and the exhaust ports.