Axel,
I think what you have there is an Aviation Products, Inc. (API) tail wheel fork, single arm variety. They also make a dual arm version:
http://blog.bowenaero.com/?p=88
I think they will swap it out for you if you call Karen at the indicated number (if you want a dual arm). Also, I believe they will ream the knuckle for you to match the end of your spring after you cut it. Talk to them. They did something similar for me a couple of years ago.
Good luck!