Print one of each of these. You should be able to print them on the stock Printrbot Simple build plate if you rotate them 45 degrees and bring the slic3r skirt in to 1mm from the part (and possibly fudge the numbers for how large of an area you can print on). They are almost mirror images of each other except that one hole shifts slightly to match the way the original X carriage tries to compensate for the different positions of the fishing line.
You may need to ream out the holes in which the rods should fit. I typically do this by hand with a 5/16" drill bit, because using a powered drill has blown right through the cap for me a number of times.
Removing the old build plate is rather easily done, and only costs you two zip ties each time you have to do so. The hardware can then be reused to mount a new, larger build plate.
The interior holes at the negative-Y side of the brackets can be used to balance out the force caused by tightening the fishing line, but I found that it wasn't strictly necessary.
You might want to increase the infill (I used 0.3 and it may have been too little) and possibly change the angle, since you'll likely need to rotate the part 45 degrees (which matched my infill angle and possibly weakened the part). My first attempt is starting the split where the fishing line is mounted and I think it is due to these factors.