Hello,
I you have posted my latest version of the extruder. https://www.youmagine.com/designs/ultimaker-block-extrusion-free
This new version, however, is dedicated to the ABS. It take into account a larger withdrawal Coefficient.
Last thing. This version is 100% free. Indeed, designed with FreeCAD, open source, and printed on Prusa. That said, it is not impossible to decide .stl with Cura to print with Ultimaker.
I hope this version will allow you to redo your extruder, better to imagine other solutions around this design.