Determine the maximum load on your drag links, multiply by 1.5 then divide by your available system pressure. The result will be the minimum surface area of the cylinder piston. Take the square root of that then divide by 1.57. The result is the minimum cylinder size. Go with the next larger size.
Load = 8,000lbs x 1.5 = 12,000
12,000
------ = 6.0
2000psi
Sq.rt of 6.0 = 2.449
2.449
------ = 1.559" minimum cylinder size, 2" recommended.
1.57
Keep in mind that hydraulic valves have a certain amount of leakage (even new) and cylinders may blow by over time so constant adjustment would probably be necessary. That's why they use an adjustable solid link.
You'd need a way to maintain the pressure inside the cylinder. Like a positive shut-off valve. This valve would have to be controlled by your action valve; Otherwise, forgetting to open it and attempting to move the cylinder would cause your system relief valve to activate. That's the scream you hear at the end of a cylinder's movement.