For the print volume restriction you might be able to split the head in half and then connect water jacket externally? I just bought a Bambu 3D printer that will do a 10" cube and if I ever get to the point of having a head flow machine, I'll be trying to model up some different port, bowl, and chamber shapes. But my CAD competency needs a lot of improvement first. Unfortunately the best I can do is some carbon fiber reinforced filiment, nothing in metal.