So, this are the parts that’ll become the headstock, including the previously thinned down flamed maple piece, matching the top of the body:

I made a quick planing jig to thin the headstock down from 20 mm to a tad under 13 mm:

Came out great! The total thickness of the sandwich is 15.61 mm, so I have about 0.1 mm left to sand off during the shaping to get at my desired 15.5 mm headstock thickness: