On the port Bucket since there is no derailer to deal with, position the 2 x 6 hard against the outboard face of the axle receptacle.
Then position the remaining two 1 x 2 x 5+3/4" with their inboard end-grain edges hard against the outboard face of the axle receptacle and their long edges hard against the axle extender.
Then drill clearance holes in the 1 x 2s for four Sheetrock screws (1+1/2" or 2") located 1" in from the end-grain edges of the 1 x 2s and screw the 1 x2s into the 2 x 6..