I used treated fir 2x6.
Centreboard rollers, I actually installed new lifting lines and inspected my rollers and pins. Mine is a 1999. There was no visible wear on the pins and very little on the rollers. I reinstalled with all the same hardware.
Trailer work floating the vessel, easy. Centreboard work not so much. I used a large excavator and lifted my vessel. I can tell you I have read about many finding a tree and using a “come a long”. I can also tell you with the back of the vessel on the trailer (strap it from sliding back) you can lift the bow enough to get the CB out and in with little trouble. Mine just cleared the trailer cross member.
I have never tried but have read:
You could, I would have to work myself up to it but will likely try one day (if I had to), step your mast and float your vessel. Grab a Halyard and pull your boat over in the shallow. I would have to have my son with me for this one. On smaller boats I can see this being easy. On our Hunter 240 with empty ballast, let me know.
Another idea have read, scaffolding. This one worries me a bit but if setup properly, it could work. Again likely for smaller boats but it is plausible.