Many thanks for posting these. Whilst we are locked down I still cannot nip out to see a friend's WBC in the flesh so to speak, so I will ask the question here.
The diagrams show the finger / box joint cuts for the lifts being parallel to the top and bottom edges of the lifts. In real life would these not be cut pependicular to the end edges? It would clearly be much easier to rout them that way.
I have always cut them parallel using the band saw and then chiseled out the wood. If you do it this way as you join them on the angle it makes for a very tight fit. Looking at old lifts they were generally cut in this manner.