I keep reading about this.
There is some concern that some early firearms left the factory with either the wrong recoil spring or a spring installed so it does not fit in the recess machined for it in the front of the slide. On almost all cases they were returned to the factory and fixed. Don't know if that is your case but I think I've read about a handful of cases on the net.
You have taken other Walthers apart, so you know they (S&W) will probably will not be doing anything other than what you are doing, perhaps with more conviction. Can't imagine you can bend the short barrel or harm the firearm while trying. Take off the grips and remove the hammer spring to make it easier. I would try it one more time with another person's help and if that doesn't work, I'd call the factory. You could remove the trigger guard to make it easier, but it is a ppain to reinstall. If you do get it apart you will likely have to replace the spring. I have a Wolff on mine and it works fine.
Good luck. Too bad you have this problem, but it seems fixable and I think once you are over this you won't look back.
Regards,
R