There is this one:
http://www.samhallas.co.uk/repositor...e_exchange.pdf
as well as the 10-line relay telephone exchange I have attached, which is also available here
https://www.americanradiohistory.com...ld-1980-08.pdf
(note the corrigenda in the following month's issue)
If I may link to another forum, the project has been discussed extensively here
http://www.classicrotaryphones.com/f...?topic=6218.60