I have the original Irmscher data sheets from when I was in the same groove as you, seem to remember I had to abandon it as the 2nd exhaust went across the back end under the bumper and won't allow a tow bar to be fitted,will be happy to post you these data sheets if you Pm me your address they are the Vauxhall/Opel/Irmscher install specs you'll need to read German, just found the exhaust data sheets for the exhaust there's a photo of the exhaust installed with bumper removed

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i want one of them 
but not at that price