Since triangles \( \triangle ABC \) and \( \triangle BAD \) are congruent (i.e., \( \triangle ABC \cong \triangle BAD \)), their corresponding sides are equal.
Given:
- \( AC = 8 , \text{m} \)
- \( AB = 17 , \text{m} \)
From the congruence:
- \( AB \) in triangle \( ABC \) corresponds to \( AD \) in triangle \( BAD \).
Thus:
- \( AD = AB = 17 , \text{m} \)
Therefore, the length of \( \overline{AD} \) is \( \boxed{17 , \text{m}} \).