It would work better aerodynamically if the Harriers were facing forward to direction of flight (i e. Pushed out backwards) although this may not fit in with your plot. Also, does plot demand the C5 has to be at speed? It would be more plausible at lower speed as there'd be danger of buffet from 300kt airflow and hitting C5 on exit.
You're doing the right thing asking us Brits; we do this all the time while we're saving the world. Some people even believe the silly cover story about scrapping all our Harriers!