The back center strip was cut out of crossgrained spruce that was cut from scrap of the top. Here's a pic of it glued in place.
I made the braces out of quartersawn sitka spruce. I radiused the bottom of the braces to a 15ft radius as per the drawing specs using a handplane, notched the center strip, then glued them to the back using similar methods as my kit guitar. I did end up with a small crack in the back (why is this mahogany so brittle?) but I repaired it. I hope this guitar will be nice and solid when it is complete! Then I used a block plane and chisels to shape the braces. Here's a pic of the completed back bracing:
I decided to make my own kerfing. It took me a long time and was quite a pain so next time I'm either going to buy kerfing or figure out a better way of making it. I ripped the pieces to width on my table saw then cut the angle on them on the table saw, which didn't work out very well - the angle wasn't consistent along the length of the strips because the thin strips weren't easy to control passing through the table saw. I used a hack saw to cut all the kerfing slots. This seemed to take FOREVER!!!
I made up neck/tail blocks and glued them to the sides. The next pic shows the rim with kerfing glued in place as well as some side braces. I was going to build this guitar historically accurate with cloth side braces, however since I already had a couple side cracks I decided to use strips of mahogany for extra strength.