There's some progress, and you are getting a look inside... the butt part. It currently looks like this:
Since there's no really clear indication of a felled seam on the codpiece, I've made it as flat as possible. The rest are felled same direction as in the Alpirsbach original.
Fitting is still to be done - and the thing also lacks the feet, which means the legs have a tendency to twist out of alignment. But that will be done next try-on session!