Action Stations 3 by David J Smith makes no mention of any association with glider pilot training at High Ercall. Halifaxes were never based there, only flown in for storage and eventual scrapping.
Halifax IIIs and Vs were operated by 1665 Conversion Unit, part of 38 Group, at Tilstock from Sep 44 and Oct 44 respectively coded OG (C Flight?) along with Stirlings to convert crews for Airborne Forces squadrons.