It would be really hard to guess at where the Structural Engineer will call for shear panels. Along with the hold-downs and their footings without testing the soil first. Spacing/size of the nails required, drag-struts at the wall to roof, etc. You could add some 1/2" ply for ease of mind. The foundation was built for the house, two story are usually 8" thick not 6". Not saying it can't be done, just not by you or me. The main beams below are for a single floor load only, may need closer piers/posts, have to wait and see. Tighten up on the screw spacing in the new drywall for shear flow in that wall as it's also rated for shear: http://gypsum.org/pdf/GA-216-2010.html
And, Welcome to the forum!