When applying the finish to a bowed psaltery, it can go a lot faster if you can do both the front and the back at the same time. Ordinarily, with a psaltery being two-sided, you’d have to finish one side, let the finish harden, and then finish the other side.
What I’ve found that is helpful is to temporarily insert just three “extra” tuning pins partially into the hitch pin holes near the corners of the psaltery. (You’ll have to drill the holes for the hitch pins before you begin the finishing process.)
What these pins do is act as a standoff for the rest of the instrument, so the finished top doesn’t touch any part of the table. From here you can proceed to finish the back and sides.