that's simple :
on your rear fender ( bottom )
ya see the brackets :
see closer :
one of them has a HOLE in the mid-section :
this hole is here for the lower bolt of the "boat-tail" .
( beehive stops end 1939 and became boat-tail for 1940 and up )
the same story about positionning a fender-light on the front fender .
see on this blog : http://milwaukeebelle.skyrock.com/