I've always been interested in doing this myself, You could mount it to an r380 box as used in the manual version of the rangy, but think you'll need the short bellhousing. The M51 motor is a very good engine, 134bhp std, but was a bit weak in the RR as the RR weight was 2t plus, so in a defender I reckon it will go well. I had a p38 dse with this engine in and that had a tuning module on it, bigger intercooler and free flowing exhaust, we reckon it was about 170bhp!