Prior to the Chevvron courses, we ran AEF for cadets using Cyclone AX3s. HQAC were fully aware what we were doing and we got a 'parents consent' form using a template from AP1919.
Monthly returns were submitted to HQAC giving the number of RAFVR(T) pilots (who had to hold a PPL[A] minimum and have 10 hours pilot i/c before taking cadets ie the same as for Vigilant G1) and total cadet flying.
HQAC indicated they wouldn't approve the Rotax 503 engine being used for cadet training however, hence the switch to the Chevvron 2-32 with its Konig engine for the actual courses.
Of course all this happened long before 'control' of cadet flying was passed to 2FTS.