The entire housing comes out and splits into two pieces, once the pieces are apart you can mock it up and see the trimming that needs to be done. After it’s properly trimmed you simply bolt the two pieces back together and it pinches the pods in place. Reinstall the housing and connect the wires.
I ordered these
https://www.amazon.com/dp/B00JK8JQSA/ref=cm_sw_r_cp_api_i_wqKRCb8PYXRDY
The factory brackets work like a clamp, two parts that bolt together so you can slap these bad boys in and clamp them down. Only reason for the modification is to make them perfectly centered.