The bus is out side security at the arrivals/baggage claim area.
It is a Blue & White (free) Massport Bus.
Be sure you get one that is marked Terminal C or All Terminals.
One of the Buses is marked Terminals A, B, Subway (do not take that one). You can always jump on a Hertz/Avis bus.
It is a long walk from A to C and it is not straight.
As u do not have to wait for DL luggage, you should have no issue if u arrive on time. U will have to clear security when u arrive at C.
Not 100% sure DL will give u your cape air boarding pass, but the lines at C for Cape air check in are usually short.