[gigi123]

Why do you want to replace the cat if the flex is bad? Just change the flex, you need to go to a muffler shop.
If it's a gasket near the cat, just replace the gasket.

 

[gigi123]

I think OEM for the side mounts are Lemforder. Front snub is Corteco. Not a big deal, Corteco is a good company, just keep in mind that the side mounts are fluid filled. Most aftermarket (read "cheap") are just plain rubber mounts.