Leave the GFs land rover alone, I guarantee you will need it before you've done building! Mine has collected lots of bits and even carried the completed chassis when i had to move building location!
If the Sierra hasn't moved in 4 months just sneak up on it at night and liberate the bits you need a few at a time. If you leave the wheels there they will never noyice th suspension is gone, they are more likely to notice if you nick the wheels
PS if you decide to do the honest thing you will need Land rover to pull it round to your place