Sailho, How did you jack up your mast. Did the loose turnbuckles give you any trouble with the mast not being stable?
I kinda covered how I jacked up the cabin top, mast, from my whole experience with this fix, you really need to de-mast the boat. To fix the counter top sag, you need to completely remove the metal compression post, the mast wires run through the post, making it near impossible to remove with the mast wires connected.
Safety, convince, and easier to work on the repair with the mast removed goes a long way with this repair. This can be a costly repair if done by a contractor or boat yard. You save plenty by doing it yourself, spend some of the saving, its well worth it, on de-masting the boat.
The repair will take you 4 or more days to complete, long time to suspend the mast of the compression post. Most experienced riggers can bring down the mast with the boat still at the dock with or without a crane.
Oh, one of my chain plate bulk heads, the forward port one, was completely rotten from the chain plate leaking, a previous owner used silicone. If you have chain plates that have been leaking, a good probability, and your shrouds could fail. My bulk head looked fine until I removed the chain plate. I was able to fix because safely because the mast was down. Another point for de-masting.
Good Luck whichever way you go.