Donal, I took a few photos last evening as I had use the boat to help out with 'Adult Sailing ' at our club. They are attached ... and hope you can read them. If not let me know and I'll send copies by snail mail.
Basically, I drilled a new hole in the keel about 30 cm down from the old hole for attaching the lifting rope (ca. 33 cm from the top of the keel) but in a parallel line down with the front and back edges of the keel so as to keep the pulling angle the same. There is steel in this part of the keel and you need a powerful drill and a good bit. Must be big enough hole to fit the kind of size of rope you need (10 ml?) and with a bit to spare to leave room to protect it with a plastic hose 'bush'. I then fed a rope through the hole so it came up both sides of the keel, the idea being that you ran these two ends over turning blocks and pulled them both at the same time ( the rope doesn't slip in the hole) so that the keel can come up between them 30 cm or so higher than before.
To get this to work you need two turning blocks fixed either side of the keel and my way was to get a guy to make a stainless steel plate bent to the curve of the old slot cover with the full slot cut out of the middle and two turning blocks welded to it at the correct place. ( Welded plates with drilled bolt holes could be used to fix standard fittings here)
The tricky bit is to get the blocks to overlap a bit to get a straight pull from below but not so close as to restrict the keel as it comes up between them.
You also need to have a thin lip front and back that protrudes a cm or so into the hole (there is a slightly wider part of the keel slot all round the top) to stop the plate slipping around.
I liked the idea of being able to lift the keel fully, single handed, while steering the boat with the tiller between my legs .... so I attached the two ends of the rope to a double block just aft of the main standard turning blocks at the side of the mast and another fixed double block at the end of the coachroof as close to the cockpit as possible, a separate rope round these giving a 4:1 purchase back to me by the tiller. Works a treat.
This all seems a mouthful .... but the photos should help. Exact measurements may not be a good idea as I think there were very small, but significant changes to the keel from time to time.
Let me know if I can help any further. I'm sure there are better solutions ... but this one developed in the making of it. It has worked faultlessly with the same rope through the keel for many years and many hundreds of lifts!
Cheers! Chris.
NB note to other readers... please ask for photos if you need them.
Chris Turner