For the people that want to know: i bought a set of new trucks for ā¬24,- plus shipping on Aliexpress and they arrivet this week.
They took quite a long time to arrive but they look pretty good and fit my wheels quite nicely. They look a lot sturdier then my old trucks. I choose one that had a simple octagon shape and as straight as possible. This way my motor mount could not slide of easily like it did with my tapered old trucks.
Now I can take measurements to design my new motor mount. With a littlebit of luck I can cnc mil it on school out of aluminium. Then I will also weld it on to my trucks for a permanent mount.