Hi,
Just a follow-up. I managed to replace the alternator bushings this weekend (I'm a busy man!), and it has 90% corrected the belt alignment.
However, the old bushings were so worn this happened, which had been making a noise I thought was the coolant pump failing:
Never ignore noises! So, I have replaced the old coolant pump as well, even though it was fine (after 200.000 miles!).