It’s easier implemented as a full school and not in a seperate programme.
Teachers design a menu of interdisciplinary projects based around themes or phenomenon that have a focus on key existing curriculum.
All non-teaching / personal time slots are simultaneous for all. This means all teachers, rooms and resources are timetabled for simultaneous use, meaning each teacher shares the load and you have smaller student numbers to monitor on either a project and mentor group.
Consider Zoning groups of classrooms into Project zones. The usual 5 teachers from 5 rooms are timetabled into the zone to each mentor their smaller number of students.
All teachers take on a general academic mentoring group to focus on learning and project progress.
Teachers share the planning and monitoring of projects which makes the measuring of progress more palatable than traditional standardised teaching and marking.
Projects can be designed generically enough around a theme or phenomenon that they can be simultaneously offered to different age groups with appropriate expectations for outcomes. This can save teacher workload.
Proposal: Changing your high school structures to match the thinking of Finland, New Zealand, Ken Robinson, and many others will halve your class sizes and stress levels.