   Inverse-Transpose.
  Is this how I compute the inverse-transpose of a matrix (in this case, the world matrix)?  My matrix will include non-uniform scales and translations.(1) Get determinant of matrix A(2) Invert A, using determinant from (1)(3) Transpose (2)   
  Yes, that's correct.   You only need to do this on the 3x3 matrix that contains the rotation and scale portions, the translation part can be left out of the computation.  The 3x3 matrix is all that's necessary to rotate a normal.   