I marked a line with the motor off showing the area you can't cut above. I was able to get 1 of the battery boxes to fit today. Take my advice and don't cut too close to that line. Mines right at the area where it might show where I cut it and need JB weld or some filler. I got really, really close.
Notice, you have to grind down both sides of the NP motor, plus it helps go grind down the lower part of the NP motor too.
This is how much material I had to remove to just barely get it to fit. It don't go on sloppy either. You have to push, pull and tug a few areas to get it to go on. I don't have time to make a perfect square hole right now I have comicon right around the corner.