They've assured me that this combination of parts will, indeed, work. I need to call Firm Feel in the next few days anyway so I'll address it with them then.
If the fast ratio idler and pitman arms don't work, I'll go with the stock style parts, which I already have, and the 16:1 ratio steering box.
If those parts do work, I'll probably go with the 20:1 ratio, which will bring me closer to the 16:1 rate anyway.