Hooking the rear brake springs on my 2 ton 1950 COE is one of the hardest things I have ever done on any of my trucks. Vice grips at right angle and pulling as hard as I can is the technique I use.
I would try using the new springs as I doubt you could hurt anything. In addition to size, the temper of the steel will determine the strength of the spring. You may find they are easier to stretch than your original one. And if they are harder, but you can re-install them, they should work. Good luck,
Kent
