Well the back box has finally fallen apart. It's been rattling and banging and rusting for ages. Well today the pipe to the back box finally rotted down to almost nothing. I have days to go.
So I've just phoned up longlife http://www.exhausts.uk.com/location.cfm
I'm going for a 2.25" stainless system from downpipe back.
I'll be thinking about better 4:2:1 manifolds, like Janspeed at a later date.