Is it feasible to create a separate cash flow for each dept manager?
That way each manager could have all the excrutiating detail they need,
and the cash flow presented to upper management could be the summary of
each dept manager. (In fact, the dept manager's performance is
probably measured by their department's financial performance.)
Additionally, adding a new project would just be a matter of adding a
new row to that manager's cash flow; adding a new manager would be a
matter of adding a new tab.

Do-able?