Front wheels – same ones as normal. Rear rain tires are narrower, hence the need for a different wheel (and the special hub/wheel combination for 50mm to allow you to run narrower), but fronts are the same width. Use a stiff wheel (cast aluminum or solid magnesium).
Also, if you normally use 65mm hubs on the front with no register, you’ll want to get a pair of 75mm hubs with the register so that you can run the front end wider.
That’s basically all we do for a rain setup – make the front really wide, and the rear really narrow. For “in between” conditions, we might run a wet setup with slick tires, or a dry setup with rains.
I don’t know what the CSC rules are, but usually the compound is open for rain tires.
Also, be sure to bring a tolerance for cold when racing in the rain…