Hi Neil, thanks for the reply/advice!
We ended up just fitting the eye and refitting the keel. We chipped a good bit of rust off what we could see. It was mostly on the top and decided it had rusted so slowly in the past 40+ years that protecting the keel from corrosion wasn't a concern. Maybe some point down the line we'll get a look at the rest whilst she's in the air.
We sourced a lifting eye locally
They had one with an eye which was too small and a bigger one(which we went with) which looked like it might have a bit bigger eye diameter than the one we removed. It was quite hard to tell as the one we removed was heavily corroded. It seems now like when fully wound up,the keel may be protruding below the stub by a few mm's. We also have a drying mooring here at Dunure, so hopefully by being impatient, we've not given ourselves problems.
Will try for a season and see..it was surprisingly quite an easy job with an A frame and a chain hoist.
Tight sails,
Lee