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If you still have the sticker on the inside of the driver's door jamb, there will be a code for the axle that will tell you. If the code is 2 numbers, i.e. 19, then it is not L/S, if it is 1 letter and 1 number, i.e. H9 then it is L/S. This is only for the rear axle though. Front L/S is pretty rare.
Before you remove the catalytic converter, do you have any kind of emission testing in your area? If you do, you should probably keep it, especially if they do any visual checks at the same time. If performance is your idea, replace the stock cat with a good, high-flow model. Still emissions legal, and better performance than stock.
If the door sticker is goen or obscured for whatever reason, there should be a tag on the rear differential cover with the gear ratio stamped in it. it will either have 3 55 or 3L55. Unless you have a different gear ratio from the factory. Either way the second digit determines whether you have an LS diff. or not. 3L55 has the LS 3 55 does not.