From what I have read, it seems that cypress did not have to age as long as other woods. It also seems that it is inherently more stable, since many old instruments used it successfully non-quartersawn and have survived 400 years or more. But, I couldn't find a source of any large enough for a harpsichord, even though it is one of the commonest trees around the Mediterranean - all the large ones have been logged. I have read a few comments that yellow cedar works very well and is stable when young, but that its sound is poor until it has aged. Nobody knows anything about black spruce.
Italian sides are part of their soundboard and are made of the same wood.
It seems that any handy softwood was used for Italian bottoms, knees, linings, braces and belly rails. I plan on using the same wood for the whole instrument for maximum stability - Ottawa winters are rough on wood structures. The best makers in all traditions cut jack bodies with the radial surface on the short side, tangential on the long side. The long side is the one that has to fit precisely in the slide to control plectrum bite, and it seems that the tangential surface stays smoother than radial under wear. The usual cupping with humidity change with tangential-cut boards doesn't occur because jacks are so small.