['29wagon]

i've not looked close enough yet and when i received my '29 everything was loose, now it's dismantled.
in looking at many photos shot at the rear i notice the floor at the inside rear fender is tapered.
i've been under the assumption that those fenders will fall into place by paralleling the frame extension "z" channels (if they are called that), paralleling them with each other. or am i seeing it wrong and the channel tapers to follow the frame .
if there is a willing folk to enlighten me on this. much appreciated .