Dont bother with the lens. its a specialty piece use by HM engineers to solve a size and location issue with leota.
For your home use, start with the projector. Get a static or even talking image of leota (plenty of places to get it online free). Project onto the wall and mark how far the projector is to the size of leota you want. use zoom if necessary or if available on your projector. Once you have that measurement, create your vacuum mold to the size face you've decided upon.
From there, work on how to either project it from the rear firing directly at the face or use mirrors to angle the image if the projector is to be mounted from below, such as under the table.
From Mr. Chicken's video, you can clearly see the projector light mounted behind the head. The only annoying thing is that the face is a little more opaque that I'd like, so from a certain angle the projector light overwhelms the image.