The busk consists of two strips of metal with loops riveted on one side and knobs on the other. It serves to stiffen the front of the corset and act as a fastening. The loops need to protrude through the seam at the centre front.
I baste (loosely stitch temporarily) the lining to the outer fabric here, and mark the position of the openings for the loops.
Stitch and reinforce between the markings, and unpick the basting. Not all of it, just the bits where the loops have to go.
Shove the loops through the gaps in the seam, press and topstitch the to hold the busk in place.
Poke holes in the other side to push the knobs through - be careful to get them lining up with the loops. press and topstitch again, and I'm done. It was easier than I expected it to be.