If you can"t find a Case cylinder, the power steering cylinder on the 700 & 900 tractors and some later Ford pick-ups is a drop in replacement w/o modification. Ford tractor cylinders were mounted up on the the left side of the engine and seem to have survived in greater nrs than the Case cylinders mounted down in front of axle. Pic is one I installed on my 310 a couple of years ago.
Some parts are interchangeable but the control valve spool has larger ends in way of the seals.
Seal kits are avail via CNH, 2 oddball seals originally worth about a buck apiece are provided for the mere pittance of $71+tax+shipping.
Cylinders were manufactured by Bendix. Some OEM parts on Fleabay.