John - Toby from BMWMiniparts has come back to me and confirmed that this part number: 188.8.131.526.932 is 70mm converter.
MIDDLE SILENCER SERIES
SPARE PART AS WELL DUE TO THE DIFFERENT
PART NUMBER IS 184.108.40.2066.932
Can any body confirm that the EU version and US version would have the same mounting points? This is the last thing on my list to confirm.
Cheers Will keep all posted of progress and what the costs would be for this.