Help!

I've been silly enough to buy an exhaust from the states, just tried all day to get it fitted and its not a good fit. The backbox is approx 1/2" short of the rear bumper and hits the seams under the boot - could this be because the downpipe is actually for a classic instead of an 02 new age? Ie is it possible to fit classic downpipes but you find they're approx 1-1.5" shorter on length under the car?

Just spent a day up API and got no where really, not APi fault, mine for buying this crap...