Do you have a defined and documented development process? You must if you are following the QSR. In this case you have the majority of the software development plan already done. The development procedures are the core of your plan. The Plan document is then the information that has not been proceduralized such as, what the project's goals are, what functionality is to be included in the project, the actual development project schedule, where documents will be stored, who is involved (often part of the schedule as well), what testing will be done, etc. I view plans as containing the information needed by the team to complete the project successfully from an administrative point of view. The plan document should be useful to the development team - it should give them information and save them from having to make "process/procedural" decisions.
62403 is written from the perspective of not requiring documented procedures. If you don't have a documented procedure for development, then the plan needs to lay out all the information that a development procedure would discuss.
