Remember that old Spiritual? Well in a way that is what I was doing today, connecting necks to tops.
You must be very very careful to line up the neck and the tone board perfectly straight or you will end up with a Ukulele with a hooked neck. Put a pencil mark at the bottom center of the tone board and a pencil line exactly down the center of the neck. A long ruler is required. You carefully cut away a notch to the outer line on your tone board and fit the neck snuggly to it.
This shows a thick plexiglas caul with two brad holes in it. When you get the neck perfectly aligned drive the brads through the top and into the neck below. Now you can take it apart, put glue on the neck and re-attach the top finding those brad holes again. Check and check again for a perfect line up.
Tap those brads back into the same holes they were in when everything lined up. Check the lineup one more time. Then slap a couple of clamps on it and and the job is done. Notice that I have put the instrument number in ink on the peg head. From now on you want to number each part. There is always individual fitting to be done and you need the instrument number to keep things straight.