I have a bit of a hybrid system mixing Toyo stainless sections, I have a mk2 6 bolt manifold and down pipe mated to a mk1 cat and backbox. all parts came from ebay although the downpipe came to ,me from it's first buyer who thought it was faulty.
Longlife are as good as the franchise fabricating and fitting them, same goes for most bespoke systems.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.
MG - the friendly marque.