Below are photo's of an alternative design from the original for this jig. Several additions to this basic Lynn's jig have been added by different people over the years and these are the results of just my take on upgrades. Some searching around the web may yeild other additions. The plans originally fell off the net a while back and I decided to preserve it for as long as I can. It is a fine design originally and that part isn't mine at all. It is well worth building. It's incredibly accurate.
In these photo's I didn't take the time to cut my stock to the proper width. You need to do that for the tops and bottoms to line up correctly. This was just some stock I had left over after making another box. That is easy to do though. When designing your box, simply let your width dimensions fall on 1/4 inch or even 1/8" increments, depending on how large your fingers joints are. I really like them at 1/4" on small boxes and 3/8" to 1/2" on larger ones. The width of your stock should be considered as well. This is just a personal preference.
Here is another link that may provide a little help on this jig.
Here are a couple great video's on Youtube by Colin Knecht of Woodworkweb.com. Thanks a bunch, Colin. I suggest watching both of those before starting on this project. Have some fun with it.