How about this one, although it covers the context of the times…. https://www.amazon.ca/Colossus-Bletchley-Parks-Greatest-Secr...

the bletchley park trust sells (used to?) pamphlets in the gift shop that they call "reports" which have been written by some of the rebuild team and other associates.

I think the national library (whatever it is called) has the actual operation manual available.

But this should be what you're looking for?

https://publish.fid-media.de/entities/book/f1548ef2-2420-4c9...