Dang...What size tire you running that you need hydro on a sami axle ?
Having driven zukes and such, id either be swapping in a toy IFS box which can handle 35s np... or be swapping in a toy axles they considering hydro with bigger tires..
Find a point on the axle tube for a reference point. Turn the steering to the left at full lock. Measure from that point on the axle to the center of the ball joint stud. Then turn the steering to full lock in the other direction and measure to the same two points. Find the difference in the two measurements and thats how much travel you'll need in the steering ram.
For something like what you're building I'd look into hydraulic steering from garden tractors with power steering. They have small orbital valves and small 5" or 6" travel steering rams that are pretty well matched to them.