I had drag radials on my old GT which was supercharged and had a little less power than my Cobra currently has. They were Nitto 555r 315/35 and were ok in the rain but they were new, but the car was not daily driven so I did not have to drive it in the rain. I would just get a second set of rear rims and throw a good radial tire on them, you don't want to ruin your car over a set of tires.