Update: If you're having trouble printing both back halves together, I've uploaded them as separate parts so they can print separately.
When printing the back half, I suggest separating out the parts into objects and setting the infill on the supports to 0%. (Slic3r and Simplify 3d allow this) This should not only improve print time but most likely reduce the forces on printing them once they get near the top.
Updated the front half to include the bridge and fix some model errors.
Updated the 'hollow' version to include the bridge.
I've added an updated version of the back half that adds additional supports for the branching arc. Note: I've not tested this yet.
The two halves have alignment holes to aid in that gluing. I'm pretty sure I made them filament sized but it's been a while since I last worked with this let me know if they're not.
Also note the 'hollowed' one is smaller than the one I split in half.