You may be interested in these two film clips. The first shows the loading of the bombs, unfused and without tail fins. Those are installed after the bomb is under the wing.
In the 2nd clip you can see a fuse inserted and how the arming wire put into the fuse and the use of a fahnestock clip to hold the wire in place. When the bomb is dropped the wire (still attached to the plane) easily pulls off the clip and slides out of the fuse allowing the bomb propeller to spin as the bomb falls, arming the bomb.
http://www.criticalpast.com/video/65...nks-on-trolley
http://www.criticalpast.com/video/65...nia_Hell-Hawks