So the thing that held me back from doing this, was i was scared the 3d scan of my face would not come in the correct scale for slimterface project. but the project accounts for this
The text guide is a little confusing but slowly made sense.
hide everything but your face and alignment guide
use the shapekeys in the alignment guide to mimic your bsb settings (ipd/perception lenses/perception lenses thickness for left and right eye/and your targeted eye relief)
Scale and rotate your head until your eyes line up with the eye relief cross section
make sure your face scan has no holes
Solidify your head to simulate the thickness of your padding
make sure none of your face mesh clips through the red alignment guide
Re-align again to be safe if it clips
Show the version of slimterface you want and use the boolen modifier on it against your face
export as stl at 1000 scale and y up axis
Print
Noideaman