Hi Gareth,
The head lift mech works on a rack and pinion, so when you tried lifting it off did the pinion come to the top end of the rack and perhaps stop there? Is the external rack bolted to the base casting in some way? If so, that would need to be undone and the head lifted off the column complete with rack and reassembled the same way. Otherwise with as much removed as possible, is it still too heavy for a 2 man lift down onto a trolley or sack truck?
Ian