rib dimensions

[ANRPiano@AOL.COM]

List,

I am replacing a soundboard in a S&S 1890s upright, more for the experience 
than anything else.  The original ribs are flat.  I was considering machining 
a crown of 60' radius into them.  But this is going to seriously alter the 
dimensions of the rib if I keep the opposite side of the rib flat.

Do I:

1) Don't crown the ribs.

2) Don't crown the ribs so much.

3) Put the arch on both sides of the rib, there by maintaining the cross 
section.

4) Or what?

Thanks for any input.

Andrew Remillard