JJmason... yes they have the flange for nailing into studs... and the headers above the windows were framed... double 2x10's I think.
The windows do bow in slightly. I'll take a pic... not sure if you can see it - it is minimal.
I was using a 2' steel square to determine if sashes are bowed or not.
Isn't this normal though?? I mean, nothing man-made is 'perfect', right?