I've got to say I'm quite surprised one would bother with a diff cooler for a sub 1000 pound trailer or strengthening the back. The stock 260z factory towbars are more than capable of pulling that sort of weight, as are its mounting points in supporting that weight and until I pulled my zed down I had done a fair amount of towing with it, with no adverse problems in Australian summers. Anything to much heavier around the 1500-1600 (750kg) mark I'd be worried about stressing the mounting points and braking effectiveness.