The more I look at the pictures of your bikes, the more I think the bracket you got is not fit for the job. My bike, which is an 1982 model has the same frame you pictured with the same welded U shaped part for affixing the old ICU.
The drawing I sent is from the BMW ETK fiche. The bracket is attached to the welded U shaped support on the frame with two #5 Allen screws; These screws are spaced like was the fixing holes of the old ICU. If you do not have two holes on the bracket you got, it is not OEM and may/would/could not fit. IMHO.
But maybe you can use one hole to fix it to the frame and, then install the ICU on it ? I think that it is somewhat important that the ICU is properly grounded so tying it to the frame may not do the job.