Viper Tank would look better. If you change the seat and leave the srx tank, you will expose the screws in the tank that the front of the srx seat attaches to. Leaving an srx tank on it wouldn't be horrible, but putting a viper tank on would make the conversion complete and give you a better looking finished product. I did the swap on mine and even went a step further and swapped my srx rear bumper and cover over to the viper ones.