One document of enormous interest is this one recounting a meeting between US President Eisenhower and British Prime Minister Sir Anthony Eden. It tells how the British not only rejected any idea of joining the EC but also intended to oppose and obstruct its creation between the then six member States. But it was President Eisenhower and Secretary of State John Foster Dulles who dissuaded the British from being obstructive. For the Americans, the EC and Euratom were essential to ensuring lasting peace and cooperation between Germany and France.
One of the striking features is the contemporaneous importance of the Euratom Treaty.
History buffs will have fun looking at the documents as there is quite a lot of fascinating material. There are lots of references to the Spaak Report. You can consult the original French text of that important document here and an abridged version in English is available here.