I paid a visit to Ace Hardware for some supplies. I found that I could use some pop rivets (Part # 2014041, 1/8") and knock the pins out of them. If I take 2 of the remaining sleeves, I can put them into the string holes on the bottom of the neck, one from the top, and one from the bottom. They are just long enough to meet in the middle of the 1x2 neck piece. I can feed the string up from the bottom and the sleeves will protect the wood from the strings while being played.
The decorative sound holes are 1/2 inch brass grommets, (General, part # 1261-4) and you get 24 of them for 5 bucks.
The 1/4 inch phone jack I got is not long enough for the thickness of the side of the box, so I need to find ones that have a longer shaft on them.
** Actually, I just decided that the easiest way to do this is to relieve the wood from the inside of the box with my Dremel tool to make room for the jack. This should be done as soon as the batteries in my Dremel get recharged.
I hope to have this prototype up and ready to play by this weekend, next week at the latest.