You're going to want the 2014-2016 Quad radiator. I'm unsure if other years for the Quad will suit, the YZF450 dirtbike radiator will not suit as it's a split unit.
It will need some work by an aluminium welder. Some lugs need to be removed and some brackets need to be moved in order to get it to fit in.
Both radiator hoses will need to be replaced with longer pieces. The LHS piping needs to be an S-bend as the radiator outlet now points straight down, not towards the engine (which the old one did). I've used a couple of pieces of curved hose with a plastic L-shape in the middle.
End result fits ok:

Two last things:
- The thermostat on these bikes opens at 65C. I've removed mine as I'm in a fairly hot part of australia, but if anyone lives anywhere warmish, they might want to consider drilling holes in the thermostat instead.
- The temperature gauge on these bikes is really untrustworthy. I've been using a hand-held infra-red temperature sensor on mine to try to figure out how hot it really is. But if you can feel significant heat around your legs, chances are it's too hot.