I am in the same boat. I was able to use the Mixed Reality Framework when it first came out be because they offered a Mixed Reality Calibration map. This sadly was not included in 4.20 and bringing it over from 4.18 does not work since they have changed many of the CPP libraries so they are not compatible.
I have gotten as far as you have and also wish there were more details since you still need to calibrate our controller or camera to the scene. 