The harpsichord kit came with a mitre box that has all of the correct angles for cutting the different joints which helps a lot. Fortunately I already know from past experience that I am almost completely incapable of getting mitre joints right the first time that I cut them so, accepting that inevitable reality I cut all of the joints with pieces of scrap wood first and then, when I have got them correct I cut the moldings to match.
Attaching the bottom molding to the bentside is going to be challenging - it is about 1/4" thick and, while it is just possible to bend it to fit the curve of the bentside it is going to be really difficult to attach it no matter how many nails I use. Eventually I decided that it would be better to bend the molding first before attempting to attach it so I built a form that matches the curve of the bentside out of two pieces of 3/4" plywood and an improvised steamer out of some 2" black ABS pipe and an old kettle. After steaming the molding for about 20 minutes I clamped it to the form like this.
I wasn't sure whether I had steamed the wood for long enough but, after leaving it clamped to the form overnight, it held its shape very well.
The top molding on the bentside was thinner, more flexible and much easier to clamp in place so I didn't bother pre bending it and just used lots of clamps.
Once everything was attached and all of the excess glue had been cleaned up it looks like this:
