@johan, Understood. Just edit the dxf’s by adding an extra 100 mm to the center of all the pieces, and get the appropriate size smooth rods. Find your bed first 300×300 is not very common.
Any reason not to use PET instead of ABS? It has extremely similar properties but much easier to print with and no heated chamber needed. Large ABS prints are going to be extremely difficult to keep the curl from happening. An enclosed heated printed is a pain to deal with.