Cranes & cylinders
Excessive end shake may due to either of two causes. The first is poor fitting at the factory and the revolver came out of the box that way. The second is due to wear. In the latter case there will be a groove in the bottom of the cylinder well that needs to be ground flat. The end of the arbor or yoke tube will also need squaring up. These two operations provide true mating surfaces to minimize further wear. Excess end shake will accelerate wear.
A variation in cylinder to barrel gap as the cylinder is rotated may be due to uneveness at the arbor/cylinder well inetrface, in which case the operation above will fix it.
It may also be due to the cylinder face being not quite square. In this case I would not worry about a 0.001 inch difference unless I seriously wanted to drive tacks at 100 yards.
The cylinder gap may be different on right and left sides due to the barrel breech face not being quite square. Again, I'd leave well enough alone.
Adding a 0.004 shim will remove 0.004 from the end shake, Assuming the arbor or yoke tube face and the cylinder well bottom are flat and squared up. If they need truing up, this may actually increase the end shake before you put the shims in. The shim kit will have several shims of 0.002 & 0.004 thickness. The shims are a hard grade of stainless that will wear better than the original metal.