Read everything that you can in your area of interest. Filling in the things that we do not know and that will help us know more: that is what research is all about. These days, sixty double spaced pages, with figures, tables and bibliography, would be a long paper.Figure out what are the important and missing parts of our understanding. Your proposal will be shorter, perhaps five pages and certainly no more than fifteen pages.A clean, well thought-out, proposal forms the backbone for the thesis itself.
Getting a good idea hinges on familiarity with the topic.
This assumes a longer preparatory period of reading, observation, discussion, and incubation. Then just write the important parts as the proposal. Our MA program statement used to say that a thesis is equivalent to a published paper in scope.
(One 'old saw' about research in the social sciences is that the finding is always: "some do and some don't".
Try to avoid such insight-less findings; finding "who do and who don't" is better.) One problem with this type of project is that it is often impossible to tell when you are "done".
It includes a model outline, but advisor, committee and funding agency expectations vary and your proposal will be a variation on this basic theme.
The same principles apply to dissertation proposals and to proposals to most funding agencies.
The proposal should situate the work in the literature, it should show why this is an (if not the most) important question to answer in the field, and convince your committee (the skeptical readers that they are) that your approach will in fact result in an answer to the question.
Theses which address research questions that can be answered by making plan-able observations (and applying hypothesis testing or model selection techniques) are preferred and perhaps the easiest to write.
This guide includes an outline that looks like a "fill-in the blanks model" and, while in the abstract all proposals are similar, each proposal will have its own particular variation on the basic theme.
Each research project is different and each needs a specifically tailored proposal to bring it into focus. In the end, they may well all be interpretations of observations, and differentiated by the rules that constrain the interpretation.