So - this morning's task is to work out how to attach the chuck to the hoist not only safely, but also so that it can be manipulated when refitting with enough accuracy to get things aligned. There are two 'O' rings squashed between the chuck and the back plate conveying the hydraulic oil, and I imagine it would be very easy to knock them off during installation as they just sit in small recesses.
I had thought to make up a rope net sling but that probably would give too much stretch

So I intended to roll up an encircling sheet metal strap that could be bolted up tightly incorporating a lifting eye, and thinking that if I could perhaps pick up an indentation in the chuck periphery (the jaws for instance) it would be more secure from slipping on the metal to metal contact of chuck to strap.
Rotating the chuck by hand, what do I see but two 'bungs' screwed in the periphery, both stamped "1/8 NPS", in what would be an excellent place to screw a plate with a central lifting eye. Taking them out they obviously block oil ways, probably an artefact of the manufacturing process but the length of thread is pretty short - are they strong enough? Now 1/8" NPS (an American pipe thread I believe) is 27 TPI and approximately 10 mm o/d. Getting out my Imperial thread gauge to check that it IS 27 TPI I find that there is no 27 TPI blade, but there are two 26 TPI blades! This is a Moore and Wright No 800 thread gauge that I bought brand new when I was at school - I remember drooling over the tool shop window and convincing myself that I NEEDED that thread gauge set ! Now it just so happened that I acquired a second No 800 M&W thread gauges set in a job lot of tools last year, getting it out it didn't have 27 tpi going straight from 26 tpi to 28 tpi. ! However it DOES have a 25 TPI blade not in the other set !
Back to the chuck. Continuing rotating it by hand what do I find but ANOTHER bung about 180 degrees from the others, this time marked "1/2 UNC" - much more promising. Taking it out there is quite a long length of female thread and 1/2" UNC is reasonably strong - should be good to dangle 47 kgs off (I hope) BUT the position of the thread in the periphery of the chuck is far to far forward to be the centre of balance. However, on the face of the chuck in the same rotational alignment is another threaded hole that turns out to be 3/8" UNC. If I can make a stout bracket that is fixed by these two threaded holes, but extends further back to where I think the centre of balance is more likely to be, I maybe have a winner, and this will be far more secure than a strap wrapped round (I Hope)
. . . . Off to hunt for heavy section large angle iron !