One trick that I use is to use zip ties from the sprocket to the spokes to strap the two tightly together as they can get seperated as you put the wheel back in. Also prize the disc pads apart to allow more space to get the disc inbetween them.
You must put both spacers into their respective positions before you offer the wheel in to it's correct place.
When in don't forget to pump rear brake pedal to get disc pads tight up to the disc.

Hope this helps.

Steve

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