The thing about the cab cylinder relationship with the cab fully raised is that the cab is basically hanging on the fully extended cylinder as the cab should be forward past the balance point. to do this safety without any unpleasant surprises you need to raise the cab right to, or even slightly before the balance point...
This is where you cut your brace length to, right at or just short of the balance point so the cab naturally wants to rest back onto the brace in compression. you then install a ratchet strap tie down from the cab back to a suitable anchor, holding the cab in tension against the brace, locking the cab in this position.
You need to put the cab at the balance point resting.pulled back against the brace to unload the cylinder to allow you to remove the top crossbolt. Once the nut is loose you should be able to rotate the top pin by hand...
Last time I did this I made a brace from the top of the rear of the engine block up to the cab latch area. the rear engine lift bracket has a hole in it to which I could anchor the bottom end of the brace. I then lower the cab slightly onto the brace, cab on truck/lowering side of the balance point so the cab naturally wants to rest on the brace by gravity. Attach a tie-down between engine lift bracket and the cab latch and pull the cab into a little more tension on the brace. The angle of the cab at the back captured the brace at the top and in tension with a tie down ratcheted down, you would need a sledge to beat it out with the bottom anchored to the engine lift bracket... a 2X4 trimmed to fit the end points properly is more than adequate as near the balance point it will see more force from the tie-down strap than it will from the cab/gravity... Yo can put in more than one if you are worried about it... Don't mess this up, because you must disconnect the front/forward tilt safety restraint bars when you disconnect the top of the cylinder, so if the cab goes over forward the only thing that will stop it is the ground...
When you disconnect the ram at the top(cab braced and restrained of course), you should be able to disconnect the line to the rod end(opposite side of the external tube at the bottom end of cylinder). Set the control valve to the cab lower position and apply compressed air to the rod end port on the cylinder where you removed the hose. This should cause the cylinder to retract and push all the fluid in the base end back thru the system to the reservoir. won't really loose any fluid this way except if any drips out of the hoses...