Quoted from OutpostKodelia:You could try gripping the vertical rail with some pliers (padded with some felt or something like that if you are worried about marring the metal) and bending it away from the ball guide, bit by bit, until the piece snaps in. Likewise you can bend the ball guide away from the rail slightly, which might be the better option since it won't risk causing any issues with the loop lane. Either way, the fit is meant to be snug, the part should barely fit through before it snaps into place. Let us know if that works, or if you don't want to go that approach, and we'll see if we can figure something else out.
Here's what I did to get this to fit if your machine is too tight of a squeeze for the Rush spinner lane correction mod to easily snap into place.
1. If you lift the playfield so you can get at the screws fort the spinner lane top ball guide, take the nuts off of the spinner lane guide.
2. This will give you enough give to then press the guide out of the way enough to press the NinjaCamp piece into place.
3. Replace the nuts that you removed/loosened for the spinner lane ball guide and your're all set.