I am impressed that that old veteran is still around. The GEC leak transformer says '140 watt sodium lamp' so it was built to take the old SO/H or SOI/H lamps, but it has a 90 watt SOX lamp in it now (should run fine). That leads me to believe that it was made before SOX was introduced in the 1960s.
in the ebay description, you said tripped the electrics. If you meant it blew the fuse it may just need a higher rated fuse to run. but if it actually tripped the breaker, then a litany of possibilities arise. There are a few qualified sparks on the site that would be able to help much more than me
Given your (and the lights) location, it is possible that someone bought this for a good security light in inclement weather. The sodium lamp is excellent at penetrating fog. If it was actually mounted in the shed, then the only real possibility that comes to mind is that they were using it as a darkroom safelight. Or perhaps they were an old light enthusiast.
Unfortunately, while I would love this floodlight, I'm still in school and can't travel far
There should be someone else on the site that will take this though