I'm doing the same protect this year. I have a meat hook I can feel when the winch is up. I would say from the tip of the 6' keel back to the fixed keel would be about 8' plus another 3' up the trunk and into the winch. But I'll measure my old one first. I can sling the boat high enough in my barn when I paint the bottom to drop the centerboard down a couple of feet and get access to the connection point.
Some of the winches have been replaced over the years and I hope not with a trailer winch. the original is clutch drive so it can't freefall. Mine goes into a serpentine on the spool. I have to get a better look at it with the winch and wire off. I also want to get a good diameter measurement. It looks like 1/4" by eye.
The centerboard connection is made by 2 tangs of metal (I think bronze) with a clevis pin through a hole in the centerboard and a clevis pin through a sage terminal at the end of the cable. I'm going to use a Suncor quick connect rigging terminal on mine. It will be smaller and smoother than a nicro press fitting so it doesn't hit the fiberglass trunk on the way up.
The biggest part of the project will be looking at and fixing if worn the guide pulley that is up in the trunk. These can get seized and stop rotating. Then the cable wares a groove in the pulley and might ware through the pulley pin. I have a 2"x2" SS plate on each side of trunk a few inches below the copper tee entrance point at the top of the trunk. I took these off to see if i could get to the guide pulley, but it looks like it was glassed over. I could see the indentation of the 1/4" to 3/8" shaft through the pulley, so the fiberglass isn't that thick there. This is close to the water line of the boat and could leak. I'm going to try to wrap a 1/4" line or cable over the pulley and see if mine is free and if not try to free it up. Catalina uses the same set up and you can get replacement pulley and kit from Catalina Direct.
I also have a groove in the copper tee at the top of the trunk. Its starting to go into the clear vinyl hose. My plan is to use Marine Tex to fill and fair the groove and replace the 2 different size vinyl hoses.
Here are some pictures of the centerboard connection.