After confirming that the top crest was even, I pinned six of the 3/8” spindles with a 3/16” cross dowel. The upper assembly is under a great deal of tension. Pinning the spindles is a sensible precaution.
Drill the cross dowel hole with a stop. It would be very bad to drill through the front of this beautiful top crest.
Apply glue to the pin and drive it in.
Trim the excess.
Next, move on to wedging the spindles below the seat…
-- Mark, Minnesota