Hi GM,
One of the first jobs i ever did on a landrover was replace the fuel pump. It was a 200tdi defender and I am pretty sure i used a 17mm spanner on the bit where the pipe goes into the lift pump (to prevent any damage) and a 13mm spanner on the nut which connects the pipe to the lift pump. As a total novice this was a relatively simple job and I remember being truely delighted and satisfied once my shiney new lift pump was in place. However it transpired that I had needed to replace the ignition switch (that was my second ever job on a landrover). Even though the original pump was knackerd it made no difference having a new one!!
Good luck with whatever it is you are doing.
Shades