Do you still have the original computer stuff still hooked up and working on your '81? If so it might cause the check engine to come on intermittently since there is a O2 sensor in the exhaust. 

If you do remove the A.I.R. pump you will have to remove the check valve at each exhaust manifolds and cap off the fitting.  The original exhaust manifolds on a '81 are tubular stainless steel and the 4 separate tubes that feel each pipe are welded so you can't cap off each one separately like on the older cast iron ram horn manifolds.

Why are you wanting to remove the pump? Just curious.