The Airship Industries 500 and 600 used Porsche flat 6 engines which drove vectored, ducted fans. The engines were in-board, (in the rear section of the gondola) and each ducted fan swivelled around the drive shaft from its engine. So the engines themselves remained static and fixed.
UPLINKER, you are correct. The gearboxes were Westland Lynx tail rotor gearboxes, and from what I recall reading at the time, they were the most expensive components in the Skyship 500. HAV would probably want to avoid the upfront costs of manufacture and certification of bespoke gearboxes and the hazards of being tied to potential competitors (i.e. helicopter manufacturers) for off the shelf units.