Full Idea
It is commonly assumed that meaning and content can come apart: the sentence 'I am writing' and 'Ofra is writing' may have different meanings, even if, as currently uttered, they express the same content.
Gist of Idea
Two sentences with different meanings can, on occasion, have the same content
Source
Ofra Magidor (Category Mistakes [2013], 4.1)
Book Reference
Magidor,Ofra: 'Category Mistakes' [OUP 2013], p.80
A Reaction
From that, I would judge 'content' to mean the same as 'proposition'.