My new exhaust centre section turned up today but it doesnt fit to my back box. the back box ive got is supposed to be a direct fit for all mk3 astra's. the o/d of the centre sectoin is 49mm and the i/d of the back box is 45mm. Is there two diff types one for 1.4/1.6 and then one for 1.8/2.0 ????? would be grateful for any info ppl. cheers