Have looked into this some more, now that I know a bit more about the structure of the rear mount - mine is the large cast item, not the fabricated type shown in the parts book. Its bolted to the base with 4 bolts. The two at the rear I can see how to hold the bolt heads while undoing the nuts, but the front 2 heads look extremely difficult to reach even with th exhaust removed. One I can get a screwdrive end onto to hold against torque on the nut, but the other I cannot see a way to reach. Are these bolt heads captive in any way, or is a special tool needed ? eg a ring spanner with the ring at right angle to the spanner stem? Crow foot open ?