Matt,
I see you posted over on Papa's thread too. Regarding buying a 580B with shuttle problems(torque converter drive), I think the buyer should generally be prepared for some major work. One should be mechanically inclined and have a good hoist. A hoist on wheels is best, I suppose an automotive engine puller may work, not sure about that.
Sometimes it's a simple fix, but one should be prepared for the worst(splitting the tractor). I think there are 2 old threads here, My 580B won't even move, and My first backhoe 580BCK. These two big threads have lots of pictures and info in them.
A 580CK or BCK that won't move could present a buying opportunity, if the price is right, but keep in mind that used parts are hard to find. That is, the parts you need. New parts are still available from Case, so far.
As I recall a good working dash gauge will tell you if the pump is working. If at idle the gauge goes up in the green, after shifting to forward or reverse, the problem is generally in the shuttle assembly itself. With the transmission in gear, you shouldn't hear a whine, like shafts moving, or the problem is farther back.
Some 580B's have a big 'R' or a 'T' stamped on the right side of the serial # plate, on the steering column. A 'T' could mean a Twin Disc shuttle assembly. These are hard to work on, and require a press, unlike the Rockwell unit.
In general, I think one should consider buying a newer Case, like the C or D model, unless you want the challenge of the older design. Phil