Santa Cruz Tazmon headset problem

Today I had planned to switch the Judy SL forks in my Tazmon for a Marzocchi Bomber Atom 80.
I've bought this bike 3 weeks ago. The seller told me that a custom headset was mounted. Now it turns out to be a threaded headset with a conversion quill mounted in the steerer tube and a ahead stem mounted on that quill.
To mount the Marzocchi I have to replace the threaded headset for a threadless one.

But first I have to take out the forks. I've taken the lockring off but the fork won't come loose. I can move the top of the steerer tube but it hasn't got any noticeable play in the lower cup and turns flawlessly. I've allready tried a tap with the hammer but that doesn't help.

I'm running out of ideas.
Anyone here has any idea how to get it out?
Thanks very much in advance.
Remko

Re:

Fixed! Just hammered the steerer a bit harder.

Well done, just what I was going to suggest!
What rear shock are you using? Doesn't look like the standard Risse one.

Re:

I'm using a SID. But the negative spring airchamber is leaking. And it doesn't use the third mounting point.
I'm thinking of mounting the original Risse. But the fully world is new for me so I'm taking some time to figure out the options.