Whitty

I have been given a Magnex stainless back box off of a Peugeot 306xsi race car and was hoping to modify it to fit my MY96.This will require having a new inlet pipe fabricated(no problem as I am an engineer and have contacts in the metal fabrication game).My question really is this-does anyone think that there will be a problem with gas flow quantities i.e will it restrict exhaust gas flow and therefore performance?