I've loaded mine well beyond what I should've done, but it's hard on the interior and kinda sketchy when you've got a log splitter aimed at your head. When I need to move something that I can't/don't want to fit in the back, I just bring a trailer. My dad picked up a homemade pickup bed trailer at a yard sale many years ago, and we have gotten so much use out of that thing. Dump runs, engines, moving boxes, floor tile. It's great. And it's half a Ford Ranger, so who cares if it gets dented up? There's no anxiety that you're gonna mess up your nice truck, provided you don't overshoot and hit the tow vehicle.
I'll bet you could get a front-end-wrecked D21 (or any small pickup really) and make a utility trailer out of that way cheaper and easier than cutting up your Pathfinder. I'd expect the leaf springs to handle the load better than the WD21 coils, too. The trailer lights could be interesting (standard four-pin combines brake/turn and D21 taillights don't), but it wouldn't be hard to rig up some non-standard five-pin wiring for that.