Snuggles, can you measure your exhaust components? All of them at the inlet and outlet? Series 1 SSE'* have 2.5" all the way back. I've measured one personally (and it wasn't supercharged).

With regards to your PM, we can't answer technical questions via PM. I get far too many requests each day, and it defeats the purpose of the Forum to ask questions where others can't see the answers.