If you can find a cylinder with the right radius, it is the best way, but it is not easy to find as it is quite big (except if you go to Phil's garden ! Couldn't we all do that ?
we could have a SS1 bending barbecue party !), But you can use the die. It did it this way, bending SS1 little by little, and checking along the way with the curve of CP11, and it is not that hard to find the right curve that way. No kink if you take your time. My advice will also be to tack SS1 and CP11 together before tacking the assembly on the chassis.
Good luck !