That's a pretty nice solution.
I've made up my mind with how i'm going to approach it - thanks in part to the information here.
I'm going to lay "train tracks" out of the hangar onto the concrete pad. I'm then going to construct a pad approx 12 feet square out of rectangle section mild steel. On the bottom will be 100mm pulley wheels to run on the rails. The top will be skinned in thin steel sheet and rubber flooring (plus aluminium grounding strips). The whole thing will be about 125mm high, reducing risk if one skid slips off.
I'll use an electric winch to pull the pad in and out of the hangar.
This is more or less the same as a system I used during some training at a private site in Brighton.
The benefit of tracks is repeatable accuracy and much lower chance of whacking a blade against the side of the hangar. If the machine isn't landed centrally, the 3 blades can be rotated to compensate.
This gives me a nice excuse to finally buy an Arc Welder and learn how to weld
