The civic radiator will work out great! Thats what I origionally planned to use on the 583, but found a bike rad, that worked better with the rotax cooling system. Look on ebay, theres a company selling all alum. racing radiators for about 70 bucks +s/h. They are MUCH better than the stockers. Stocker rad's have plastic end tanks, and aren't very thick. If you go with an aftermarket all alum radiator, you'll never have heating issues.