Hi Ola,
I can confrim what Ken S says for 235s and 275s, The 27 keel is lighter and the wire strop at it front can be used as a depth indicater (put a 'flag' at the top of the wire and run it away with shock cord. The Keel of the 27 can be locked up using a bar or bolt through the two side holes in the keel box and the large hole in the top of the keel.
The wire strop can also be used to lift the keel (circa 375lbs/160kg) out of the slot if you have a crane/gantry or high strong point to lift from.
I have stopped using grease on my keel as it goes 'claggy'with sea water and mud. The teflon (McLube) works for a while but mud soon sees it off.
Another mod which works for me is to fit a second wheel in the top of the keel in the same way as the original and fit a second stand-up block on the top of the keel box which has two rope holes one each end of it. My lifting rope now runs as originally fitted, but then goes over the new keel box block, down to the second keel wheel and then back up to the keel box where it is dead-eyed with a knot.
This gives 3:1 purchase in the box so it is possible to lift the keel manually - just!
Only disadvantage is more rope in the halyard pockets.
Cheers
ChrisN