All this confusion seems to have been created by Ford.

Some of the part manuals (as NumberDummy stated) only show the 205. I have an exploded view from Ford (dated Jan 75) that IS the Dana24 but does not ID it that way. (the 203 and 205 both have a large ribbed cover on the back of the front output shaft) The diagram can be found here: http://www.fordification.com/tech/im..._64-72F250.jpg
(I'm not sure if I'm allowed to post it here)

The Ford issued diagram does state that this transfer case was used in 64-5 in the F100 and 64-72 in the F250.

It looks (to me) like someone at Ford writing manuals saw
"chain drive t-case = 203"
"bronco t-case = Dana 20"
"gear drive 1-speed = Dana 21"
"gear drive 2-speed = 205"
and completely missed the Dana 24. Aftermarket suppliers rarely double-check the OEM.

Jim