What I see in the overall system of the GSM Company is that they problem in the system itself. Low profitability, productivity and management/staff relationships happened because of lack of training and proper orientation in the roles they have. The top management also failed to clarify the vision/ mission and objectives of the company. This has resulted into confusion and autonomy of actions that leads to lack of teamwork and camaraderie in the organization. So I suggest that lack of vision and leadership, orientation of the roles and responsibilities should be included in the first question.
While you have successfully elaborated the possible OD interventions in the group, I suggest that you should further specify the exact ways of intervention. For example, you have indicated that one possible OD intervention is Group Intervention. Instead of defining what group intervention is, it would be better if you will indicate particular action plans such as conducting a group dynamics program or you would initiate personal role/ responsibility re-orientation to each of the top managers of the organization. You can also suggest a training for the top managers and even the middle managers on leadership and productivity enhancement, critical trainings for managers and leaders that a 3rd party Organizational Development can do.
In my opinion it is better that you will indicate the breakdown of steps of action that you will take upon intervention. Again the key in a successful Organizational management program is the organization of your action. Also logical and chronological arrangement of actual modes of action that you will carry out should be clearly emphasized so that you can clarify the top management on what to do first.
I think it is better if you will create an outline of your change management team, starting with assigning people in the teams that you need in managing your intervention. Then, you can indicate the possible areas that you will tackle in your intervention. For example, on the production team, you can create a tailor-fitted training program. I think the best way to write your outline of preferred intervention is the actual one that you will present to the top management of GSM instead of writing general ideas for your intervention strategy.