The problem is the Superbes have steel rims...and even though the kool stops are going to be a noticeable improvement, they're still going to be pretty terrible in the rain. Brakes and braking surfaces are one of the areas where, IMO, C and V love should always take a back seat to realism. If you want the Superbe to be a show bike, keep it as original as possible. If your plan is to seriously ride this, I'd either change out the rims or try and figure out other options (like a SA coaster and 3 speed hub).
Or...of course...there's just avoiding wet conditions and being very careful when you're in them.