Yoyo: Sadly I cannot respond with any certitude on this matter, the best I can do is to hazard a guess and which is ..
.. that they probably used the areas denoted by the white rectangles in the aerial view above.
As you say, the M2 bridge was nowhere to be seen and so the westerly of the two suggested take-off areas may have been the preferable location (in fact right in front of the factory). The more easterly option could also have been used most especially (and probably) at high tide.
If anyone can confirm the above that would be grand!