I liked the concept for the presentation a lot but sometimes looking at the yellow pages seemed to go on a while, particularly in the second set of letters. The use of media such as the newspaper article was a really nice addition and perhaps could be use to augment and break up the longer segments of dialogue?
In the O'Sullivan letters, the use of dates might help provide an idea for scale of the time frames, it would also be unusual to send letters across the sea without dating them, I feel.
Also, I feel the use of vernacular in these first letters could help build an idea for the character more. The content seemed to set O'Sullivan up as a poor, working class Dublin boy, but I can't imagine such a person casually using words like 'obfuscate' in a letter to their parents.
During the Luca and Castelli bits, initially I thought it was bordering on cliche but I changed my mind as I read on and really enjoyed it. The phrase 'dead-Mick-storage' made me chuckle! A nice section.
I enjoyed the UIU report greatly also, I found it's presentation to be a nice change of pace compared to the letters and I personally find fifthism to be a very interesting part of the SCP universe so I enjoyed this section narratively also. I do question why 8 (+ 1) women were sacrificed by fifthists however; why not 5? I may have missed a trick here.
Bonus points for mentioning Liverpool (my hometown!) however I should mention that the University of Sheffield is in Sheffield, not Liverpool!
Where I struggle is piecing together the narrative, this is probably my own ineptitude and lack of sleep so potentially disregard this last point, but I don't quite follow what exactly happened, I follow the gist but I couldn't necessarily pull together an exact chain of events with a concise, satisfying end point.