Cat Converters

This is a tough question but maybe someone that works in a shop can recall. Is there any difference between a catalic converter for a 2000 GSR and the one that's on the 1994 LS? I need a cat bad and I found one for a GSR on eBay. Also, there is some kind of gasket you need when replacing the cat. How much does that thing cost, and is it really necessary?

Im not sure about the first part, but yes there is a gasket you should replace & possibly spring bolts. Gasket is like $10 & spring&bolts are like $10 each(2 needed)