My 300 90 is an early one ('96) so had the middle and rear silencer with no cat at the front. After routing around under my dads 90 ('98) which has a cat I realised that I could fit the middle and rear pipe part of the cat system to mine, which is all the de-cat pipe is anyway.
So when my middle section died 12 months ago I did just this and it seemed to give me abit more power, better respons (getup and go) and a nice but not obtrusive note from the rear.
Mark