here's a few diagrams from the donor, provided from the bmw parts catalogue, hopefully this will help.
overview showing pump, rad and pipes. What isn't shown are the 2 aluminium pipes which run from the back of the pump to the rear water rail. These are shown in the second drawing, marked 4 and 6.
detail of the rear water rail. the port near bolt marked 3, is the one I have blocked up. The expansion tank is connected to the port marked 1.
and the original setup of the expansion/header tank.
