Well despite your post gpnewhouse, you don't have fenders that curve on two axis, even if you think you do. Sheesh
Anyway if you do an English wheel is the best way to accomplish that if you want something that doesn't look like a horses arse when you are done. Another way to make the bend is make wood molds from the original fenders and hammer the snot out of it. That is sort of an art form too. Might want to practice some, you could use aluminum instead of steel, bends easier depending on the mix and hardness. O bends easy but real soft, T-3 might work. You have to make sure you do the sharper bends against the grain.