My thanks again to those who have felt able to make suggestions. After an immense amount of time spent on this, even having taken the matrix out again, today, after my second attempt of the day, I think I have finally got the darn thing in place. I made up another bolt, longer than the original to give my some purchase and a chance at starting the thread off, and then pinching the clamp. I will not know until I can put fluid into it, which after the annoyance of all this, I have put off until the next spell of better weather.
The "W" clamp is as suggested behind the black gunge and I tried taking a picture using a mirror, another suggestion from a member.