Hi williamtd50, I'm not very familiar with discoverys but on the older series rovers and early range rovers PTOs came off the gearbox mainshaft through the transfer case. If you take off the round cover by the side of the transmission brake you will see the mainshaft where a PTO could be fitted. To get a slower driving speed you could alter the low range transfer box gear which would be after the main gearbox and PTO also you could keep the high range ratio the same for normal road speeds but that would require new transfer gears to be machined and alterations to the transfer case. You would also have to gear up the PTO separately as LR engines do not rev very high the Tdi motors top out at about 4500rpm. You could also change the axle diff ratios but that would alter road speed in high range as well. Here is a gear calculator that if you can find out what transmission you have you can get an idea of what may work best for you. I hope this helps a little.