Suppose I wanted to fit a straight thru......
 

I currently have a standard setup on my bugeye wrx, bar a mongoose straight swap backbox. As well as the reason later in the post, I want more noise, the mongoose on it's own is burbly on idle but never gets any more roary once moving.
Can I remove the standard catted sections, leaving just the downpipe with a cat convertor and sensor? I have a classic non catted uppipe waiting to go on also.
I have spent around an hour searching for a definitive answer and while one guy has said he ran decatted for two years with no remap fine, I will eventually get a remap so cheapest solution isn't necessarily what is driving my questions.
I do have a leak somewhere and best guess at the moment is uppipe and or it's gasket. Help!

Bump for the knowledgable hung over saturday crowd :)