67 dart convertible trunk torsion spring length?
On left is what it is supposed to look like, Center is mine, on right is yours (flipped) but you can see how far the rod is moved
I bet the problem with your springs is not the spring is weak but the hole they should ride in is 1/2 to 1" back due to metal fatigue. My 67 convertible has the same issue but the brkt is worse than yours. if you haven't welded anything yet I would temp a brkt to move the elongated spring hole forward to its correct position and reinstall the springs.
On left is what it is supposed to look like, Center is mine, on right is yours (flipped) but you can see how far the rod is moved
I bet the problem with your springs is not the spring is weak but the hole they should ride in is 1/2 to 1" back due to metal fatigue. My 67 convertible has the same issue but the brkt is worse than yours. if you haven't welded anything yet I would temp a brkt to move the elongated spring hole forward to its correct position and reinstall the springs.