The Zerda Front gearbox is now perfectly matching at the front too : the difference of angle was 2.5° from what I estimated initially.
As it was the only remaining thing to validate, I checked it by putting the part on my screen, and it is lining up (and for those having a doubt on the method : the printed (wrong) part was lining up with the drawing before I started

). I'm now 100% sure it is right, and I did not even considered printing it
I may print the bottom part of the belt cover for the Zerda : the chassis flexibility may have impact on some measures. Beside this, taking into consideration the situation of the different parts I drawed and where are the potential mistakes, I believe the risk is very limited to have something wrong (and with a very limited fonctional impact).
The 44B chassis are rigid, and flexibility of the Zerda might be bad and good at the same time : flexibility helps traction, but the other side, not being rigid enough is making the belt skipping from what I've discuss with friends. Considering reinforcing slightly the chassis to reduce the flexibility in the belt area... Need to think about this...