Attach at the chassis end of the control arm. You keep your original bushes (or put in new original nissan bushes, which definitely are better than any other bushes you can buy for a patrol). The drop box basically becomes the new attachment point for the rear of the radius arm,which is lower than the chassis rail, and the point is to get the arm level again, as per factory, which re-sets the caster to within factory spec.You order them with caster set to your lift spec (ie:3Degree),.. the other cool thing is that the bushing on the chassis side is no longer compressed , which allows for better travel and less bind up, due to the radius arm sitting level
Note: Drop boxes mostly only needed for anything above 2"lift,.. 2" or under - not really going to work as you will end up with too much caster which will make steering very heavy.
Caster Bushes :
Attach at the diff end of the radius arm and take the place of the original bushings, they have off-set bores, which is what allows the arm to sit closer to factory spec tolerances. Bushings are known to be harder (firmer) often made by nolathane or similar material, NOT RUBBER,.. which is why it has a slightly different feel/flex. Yes, you wont loose heaps of flex, but there is more bind up
Caster Plates: (What rob is talking about)
Achieves similar result but not regarded as good as the above two by most out there. Plates get bolted to the existing holes on the axle portion, these plates have predetermined holes where the radius arm will bolt through, to create the 3" caster required. The one cool thing about the caster plates though is that you can actually create one that articulates to create a "superflex" , this only on one side, the other side must be fixed to the plate as stated above.
Generally speaking, after reading thousands of hours of info over years,... is that Drop Boxes are the best result when searching for a factory drive feel, whilst retaining Nissan Rubber Bushings, which are regarded as superior to all others.
Anyway, just my opinion based on lots and lots of readings, each person must make their own minds i guess. I'm getting drop boxes into mine in the next few months. I cannot keep driving this vehicle like this as it can be very frustrating.