Saw your post on adapting a BXA to your new lathe and it gave me confidence to tackle mine. Just bought a Sieg Runmaster 330x 1000 lathe and it had a old style toolpost with a insert post. No T slot in the compound like American machinery.
It had a european post similar to yours. The shaft was 16mm but the Boss at the bottom was 25mm and had to go. Decided to make a new post from scratch.
When I removed the compound it was obvious that the post was a press fit with a roll pin to stop rotation
I pressed it out and machined a new one. Luckily I still have my old Sieg SC4. Started with a 40x140mm piece of 12L14 and my little lathe was required to remove most of it. Single pointed the 16mm thread. The 25mm boss is now shorter and does not protrude above the top of the compound allowing the QCTP to sit down on top of the compound.
New Phase II BXA in place