NO drilling for the walkway is necessary as the holes are provided in the casting.
You will have 3 options for underframes.
1 use the correct 3D printed one with Fox Valley metal wheels
2 supplied with Aust-N-Rail GY underframes
3 use your own already purchased Aust-N-Rail underframes or what you are comfortable with
Kits will weigh the same as GY’s already out there for ease of use but you may add extra weight if you like.