I have a set of 20 inch L322 wheels on my 2001 P38. they fit fine and look real good.
You do need the nuts from the L322, but they fit a p38 perfectly well.
You will also need a set of 'spiggott' rings as well, which should be fitted initially to the wheel > not the hub.
The only problem you may have (apart from the enormous price of replacement tyres) is if your Rangie suspension ever drops onto it's rubbers. It is still drivable (just), but the front wheels wont have much of a turning angle and to take a normal left hand turn, will involve something like a 3 or 4 point turn.