Thats no true mate, mine fitted perfectly with the SI's mid section.
lol ill have a looksee tommorow see if its the same basic shape
my old Si had a janspeed GTi back box on it, and i needed the GTi centre section for that. if you can get hold of one, the janspeed back boxes are great, not too loud and nice and subtle, plus there really really well made, couldnt fault mine at all and it was 2 years old when i got it iirc.