The documentation explains how to replace the hosted engine with the distributed binary (xr.js), but I noticed there’s no mention of XR Extras or Landing Page scripts.
xrextras is not required (either technically or legally)
We don’t have an official open source release for it yet, but you can obtain it by either exporting an existing project from 8thwall.com that includes it, or I have an export here: GitHub - cmbartschat/placeground-aframe available to pull from - you’ll need both xrextras and xrextras-shared-resources.