It is critical that the wear plates or thrust washers as you call them be clean, wear free and installed with the proper clearance or the pump will not develop any pressure. These should be bronze faced steel plates. Oil will slip past the gears if too loose and the wear plates will score on the gears if too tight and lock up the pump, ruining it. Also important that the check valve be re-assembled in the proper manner. The "arm" as you refer to it is the piston rod, the "cannister" is the cylinder barrel, the 'lid" is the cylinder head and don't be surprised if the rope packing you used leaks. you claim a 6" cylinder head seal but I'd expect this to be a 7" diameter cylinder with approx 15" stroke. Six inch cylinders were not generally made in twin arm design unless twin cylinders were used.
For whats its worth this type hoist is known as an underbody twin arm and it torque curve is at it's highest at the initial push and drops off pretty fast as it goes up. From the look of the pump I can tell it's pretty old as the manifold style attachemnt went out in the 60's.
The Galion Road Machinery Co. made the loaders and other stuff.
This hoist was manufactured in Galion, OH by the Galion Body Company, long extinct but the survivor company still exists as a brand name only.
Good Luck on your rebuild and KEEP IT CLEAN and use fresh hydraulic oil.
