Note that the 1980 and 1981 Cataltic converters are slightly different. The 1981 cat came from the factory with the rear flange being cut, as if it was sawn off. The rear flange on the 1980 cat is smooth and uncut. The top photo here is of a 1980 cat and you can see the smooth rear flange in the foreground. Note the smooth curvature to the left side of the flange. The photo below shows an original 1981 cat and the flange is in the foreground. It does not have the smooth curvature and in fact looks like the curved section has been partially cut off. This makes it difficult to find an original 1981 converter since the 81Z has the unique cut flange.    The air injection manifolds are not painted black or any other color.  The original ones have a nickel or light chrome finish.  The left side is different on a non-air conditioning car verses a car with air.  The check valves located on each of the injection manifolds are plated with the gold cadmium finish. The tube which connects the cat to the emissions system is also next to impossible to find.  There was one on EBay recently for $250. This tube is routed to the catalytic converter from the smog pump.  This steel line is chrome plated and injects air directly into the catalytic converter.