As expected I had to fiddle a bit as I am using Spectra instead of belts and replaced the pulleys and idlers with custom printed ones (well to be honest, I got them from Thingiverse). As it turns out the pulleys I had printed are not exactly the right size (scotch tape can do miracles in times of emergency; still not something to keep). Nevertheless job for the day done!
Note to myself: "design your own pulleys and idlers")
Airprinting a Rostock Platform