Professional harpsichord builders would use a go bar deck like this one from Michael Johnson's web site.
Kit builders usually end up having to use nails to hold the board in place while the glue dries, but after my experiences with using nails to secure the outside moldings to the case I have come to the conclusion that, while an experienced craftsman could probably do a very good job just using nails an amateur is probably better off using clamps if at all possible.
Even though I still have a long way to go before this instrument is finished, I am enjoying the process of building it so much that I have a feeling that it will not be the last one that I build and that makes it easier to justify buying a "few" more clamps as an investment ...
After carefully measuring several different types of clamp I came to the conclusion that a 12" Jorgensen light duty bar clamp would work both for this harpsichord and also for any other instrument that I might build in future.
So, finally, here is the soundboard being glued in:
There are a total of 51 clamps - 39 F clamps around the edge of the case and 12 small C clamps in the gap between the soundboard and the wrestplank.
I used liquid hide glue for the soundboard - not so much out of any desire for "authenticity" but mostly to take advantage of its longer open time - it took me almost exactly 20 minutes from applying the glue to tightening the last clamp.
