Supremely Ghetto rigged...
 

...exhaust. Yea, so i need help. My old exhaust (which was mended and not very well by the previous owner) failed at the weld joints and fell off for the most part. So i had it in my shop class, removed the old one, and then installed my Corksport catback, well mostly.

So the pipe the last guy used to weld with is entirely too small for the new pipe, and it didnt have a flange to bolt to. so that it pretty much sitting in the new pipe tired down. And when trying to remove the cat a bolt stripped out and now even with it fully tightened its not completely sealing the cat.

In short, im not entirely legal and need help, who can offer advice?

Have you tried taking it to an exhaust shop? Fixes like that are generally pretty cheap.

Agree with above. Any decent shop can do it. I had a local Meineke or w/e weld mine up, or just slap a soda can on it.

Sounds like a job for a torch. If you were around socal I would say come on by my garage and we could have that puppy off in a few seconds. But exhaust shop is your best

If you can't get the nut off, use one of these to split it. Then replace the bolt to seal the cat. Then you need to find the correct size flange. I don't know what size it is, but Mazdatrix has a fair selection of exhaust flanges. If you can't find it there with the correct bolt pattern, then check the china store (ebay). Then find the proper size adapter and weld it all together. There's only one way to fix anything, and it's the right way.

so previous owner welded straight to the downpipe/exhaust manifold?

Get a cut off wheel angle grinder and cut the bolt head off, you will need to replace that bold anyways.