I have not done this on a Castomatic but have used the technique on several stuck tractors. Put the transmission in neutral and engage the power take off. Next put an old coupling on the power take off shaft. Then I use a pipe wrench to twist in both directions. Take it easy on the force.
I am reluctant to use the hydraulic method for fear of doing damage. If more that one piston is stuck and the one you are working on breaks loose, the remaining stuck piston then gets all the load. I know of folks who have damaged rods this way. Also, it is relly hard to gauge the amount of force you are appling using this method.
The secret to freeing stuck engines is to be very patient and relly watch how much force you apply. The old soak, apply force, soak again etc will eventually work.
I would appreciate any comments on my suggestion from others.
Thanks