BBC
Bbc News: Pakistan's Army and Its History of Politics
This site from BBC News contains a medium sized article in Pakistan's History in Military. About half-way down the article is a somewhat comprehensive exploration of Pakistan's military coup, led by Mohammad Ayub Khan in 1958.
Other
Story of Pakistan: The Constitution of 1962
This site from The Story of Pakistan explains the time leading up to the military coup in Pakistan, and the eventual suspension of the constitution. Mostly centering on the Constitution of 1962 set up by Ayub Khan.
Other
Bernard Safran Time Magazine: Mohammad Ayub Khan
A portrait of Muhammed Ayub Khan, President of Pakistan, during his presidency from 1960-1969. This site includes a link to several Wikipedia entries on Khan as well for further research.