Conversion took place at Eastleigh Works. The driving vehicles were gutted internally, whilst the coach sides were extensively modified to emulate the profile of the Mk 2 stock. Three sets of double doors were installed down each side for rapid loading / unloading, and a conductor's compartment was built into the non-driving end. The suburban cab front was retained, along with the front motor bogie, which provided 500 HP to the vehicle. The rear bogie of the vehicle was also of 2-HAP origin, although was non-powered and intended purely as an extra pick-up from the third rail. The cab controls were updated to suit multiple working with the Class 73, allowing the latter's power to be governed from the cab of the DMS (a system of which was already in use on the Bournemouth to Weymouth line using Class 33/1 diesels and 4TC stock). Conversion of the DMS vehicles was completed at Eastleigh at the start of 1984, the first being delivered to Stewarts Lane on 6th January of that year; the final members of the type arrived in early March. The vehicles became known as ''Class 489'', accompanied with the abbreviation GLV (Gatwick Luggage Van/Guard Luggage Van). Allocation of Class 489, 488/2, and 488/3 fleets was to Stewarts Lane.

In March 1984, Class 33113 hauled a 488/2 and 488/3 set, accompanied with a BR Mk1 Blue/Grey Brake coach, around the country to promote the new train. The ‘’Gatwick Express’’ branded service commenced between Victoria and Gatwick Airport on 14th May of that year. It provided a non-stop train over the 27-route-miles, taking thirty minutes (an average speed of 54-MPH), and services left every fifteen minutes. From the outset, the operation was part of BR’s InterCity Business Sector (formed in January 1982). The stock was appropriately painted in this sector’s ‘’Executive’’ livery and became the only InterCity service to operate wholly within the confines of the Southern Region. The carriages carried the legends ‘’Victoria-Gatwick’’ and ''Rail Air Link'' on the lower body sides. Seven Class 73/1 Electro-Diesels were initially allocated to the service, but these were not painted in InterCity colours from day one. Indeed, in 1988, the Gatwick Express received an official allocation of twelve locomotives, which were modified for 90 MPH running and re-designated Class 73/2. This fleet was later expanded by the addition of a further two locomotives of the 73/2 subclass.