Congrats. To help with the mud in the radiator, what I do and a lot of cross country racers around me do, is either make/buy some fairings for it, or tape the front bumper completely up. I've never ran 800km with out washing, so I do not know if this would help completely, but I do know I've never had a problem on my 450s or the XX for a few days with out cleaning, even riding in down pour conditions. The 450s I have fairings, the XX I use tape on the bumper. This prevents a lot of dirt/mud coming into the center of the radiator, but still allows air to come in. Also, if you can't clean it, can you change parts out on it? I've seen guys use outerwears on theres, they fabricate a bracket about an inch (2.54cm) or so from their radiator and put outwear material on that. There is a race this weekend, I will try to get a picture of someone that does this if any show up.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!