That really looks like it should be ok in a "tuned" gun. Might try replacing the strain screw with an 8-32 socket set screw and use that spring. The socket set screw will allow adjustment. Screw it in until you get reliable ignition shooting DA.

A 3/8" long set screw should be right. Loctite it after you get the gun running. Same proceedure will work with your Wolff spring. Then you can play with rebound springs. How much rebound spring you need is proportional to how much mainspring you need for reliable ignition.

You can (pretty) easily get a sub 8 lb DA pull (with a stock hammer) that will fire the hardest primers.

What's a Wolff LE spring and rebound spring pack? Never heard of it. Got a link?