It's easy as pie!
Trim the edges down so the lamps sit flush. Drill the middle hole out about 15mm, where the middle bolt from the lamp will sit.
On the n/s lamp swap over wires 1 and 2.
On the o/s lamp swap over wires 4 and 5.
Also on the o/s plug trim the notches off and turn the plug 180 Degrees so its the wrong way around. Would not take any longer then 30 minutes.

Rob