All the original AAR Cuda and T/A Challenger I've open the hoods on would not stay up either, you had to hold them up yourself
I have seen guys change those springs to get the hoods to stay up and the hoods will start to bend at the end of the hinge, my original hood was like that when I bought it used from another T/A owner so I would use a saw off broom stick to hold the hood up when I wanted to check or work on something under the hood
Same thing on my old Duster with a race weight lift off Duster hood with a 1968 SS/AA scoop made on it, I molded in some aluminum T on the rear to use the stock hinges with the springs removed instead of having to worry about it using it as a lift off hood