The best setup is to have the stock carb bore out to a 42.5 mm by DR. Q at quadracerhq. If you have a stock carb in good shape its also about the cheapest way to go also. The next best is to have 39mm keihin bored to 40.5 by esr but that is costly especially if you have to buy the carb from them. I have not ran a rxd 42.5 mukini carb but I know that is the fastest setup. I have a 39 keihin on my 500 and i love it but its just piped with the carb. DR. Q website is
http://quadracerhq.com/index.htm. With the 530 you will defiantly want one of these two options. Good luck