Papa,
As I recall, the large shuttle cover can be removed with the tank in place, but the pick-up tube has to be unbolted, then rebolted when re-installing. Very very difficult. If you plan to remove this cover, I would take the torque tube out the front with engine attached. Leave the tank in place, but remove the front tank studs by double nutting them. I believe the rear tank studs have to come out to, but I'm not positive about that. The steering column can be hoisted up 1"or so, with a small hoist attached to the top front of the cab.
I'm not sure about the seal kit, but get all the seals from the Case dealer if you can. You might be able to get aftermarket, not sure. If you are going to reseal the shuttle assembly, then I would clean the screen, replace all valve body gaskets, replace the pick-up tube gasket, pump seals, and clean out the bottom of the torque tube.
If you choose to remove your tank, either to remove the cover, or make engine/torque tube removal easier, it is covered in the "my 580B won't even move" thread. Phil