I would start by doing a full rebuild of your stock calipers and see if there are sticking pistons or guide pins. That would be the most likely culprit of overheated brakes, that is, if you are not constantly on them or are regularly towing heavy loads/in a hilly area.
Other than that, if you do the conversion to a set from a 300 AWD, I'd love to see it. I suspect that you will have brake proportioning/balance issues though.
andrew.wenmoth wrote:
Cant use a larger diameter or you wont be able to get the caliper on
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He can build an adapter easily, it's a very common way to install a non-OEM caliper.
I'd say the easiest upgrade is to rebuild your calipers, ditch the dimpled rotors and get good quality white box rotors and a set of good semi-metallic or ceramic pads and call it a day. Dimpled/slotted rotors are unlikely to offer the braking advantages that I think you might be looking for. The dimples are there to relieve gas pressure build-up between pad and rotor during extended braking at high speeds or if you are towing. Even if you do either of those, you still need your calipers to be working properly to not end up with warped rotors.
Don't forget you also lose all of those dimpled and slotted areas as a friction surface.
There are trade offs to both. Summary: check proper caliper and other functions before throwing money at it without knowing what the actual problem is.