Might have a bit of a quick look at the axle mounting. You've shown a photo of a little plate with a slot in it. There should be two of these. They go on the adjustable side of the rear axle bearing mounts. They give extra friction/support to help prevent the axle bearing flanges slipping in the adjustment slot. The reason for the axle adjustment is so the chain can be tensioned. Note that the axle needs to be adjusted evenly to keep chain alignment.
This is a bit out of sequence really. You won't need to do this until the chain is on. I'm just mentioning it here because we are looking at the drive train and I just happened to notice them in your photos
