Hi Tony,
Another thing to think about...there should be drain holes in the winch motor (probably located where the motor mounts to the drum). You may need to unbolt the motor from the drum and rotate the motor on the drum (including resealing) to ensure that the drain holes remain as drain holes and not, in fact, holes which do a great job of working as funnels....
Similarly, the clutch lever on the gearbox - it may be necessary to undo the gearbox and rotate the gearbox to the correct location for your installation.
Usually these instructions come with the bullbar installation manual. Perhaps someone here with a Nissan bar still has the manual?
Often it is easiest to remove the bar, lay the bar "on its face" and install the winch that way. Not from a weight perspective, just from ease of access.