Make sure the actuating arm is in the right direction for the brake rod to attach to( a push or pull).
If you can, slide the sprocket and disc over a bit, put the actuator half on the bracket.
Move the disc back, and replace the other stationary half of the caliper.
Bolt together.
Don't for get to bolt down the disc to the axle(A second look, looks like your axle is a hex shaft? It may really not much a matter as it can't spin on the shaft so not much a problem) ; And especially don't forget the little bullet rod(the domed end towards the actuator arm).