Interesting read. Unfortunately it was not the type of alignment I originally thought it was going to be talking about, but still would be a handy jig to have.
I have a jig almost exactly like this but I use it to align the beam through the air assist nozzle. It also indexes to the side of the nozzle and also sets the FL.
I put a piece of tape on the base and shoot the beam to see if it hits true center. If it is offset from the calibrated center I know the beam is coming through the nozzle at an angle.
Travelling so no picture.
I now do the same measurement with my lift table by lowering and raising it and watch to see if the point where the beam hits wanders.