I added another gear with a hollow shaft in the middle to route the z-axis through.
Had a look at nema17 motors with a hollow shaft, but they unreasonably expensive, at least with a hole >10mm.
Z-axis in the middle of the assembly makes the overall footprint smaller, but limits your bed size if you want to be able turn around the whole pole.
For a multiple hotend setup a small bed would be okay, since this way parts on the bed can't collide with the other nozzles,
because individual build areas don't cross eachother.
After the rebuild the testprint came out skewed, not sure what caused this.
The gear ratios shouldn't have changed. Maybe the pen/bed was slipping, have to investigate further..