I do not think you can fit a rear PTO to a defender. Yes the the cover plate for fixing it to the gearbox is on the back of the transfer box, but there are no holes in the chassis or rear cross member to allow a drive shaft though. If you look at the rear chassis cross member on a series vehicle, just to the left of centre is a round hole. this is for the rear PTO drive shaft, this feature is not present on the defender. Have a look at yours I may be that it is present on very early 110's or that the cross member has be modified.