long tine reader ,first time writer--short story long,i'm completing a restoration on my 200k 95 sse.i believe it was in "limp home mode"for a while before the wife let me know or that i even heard of it before i started reading this forum.I know the cat is cooked(it rattles and parts are in the muffler. I have swaped the engine with a crashed 99 3800 ,hoping that was caused it to run bad has magicaly gone away.Now it leads me to the big question,what is a good source for a new cat ,and will the car run to test if all my work has payed off?

I got mine from ZZ performance. I think it'* about $70

will it run with the bad exhaust just to test ?or shoud i wait?

You will have to clean out any loose parts and fix any holes, but it should work just fine.