I was specifically referring to 1971s.

According to:

http://home.earthlink.net/~mopared/productionchange.htm

"8/20/70: Code D21, 4-speed transmission, is not available with 198, 225, 318 or 383-2v engines. "

I guess there could have been a few 1971 four-speed 318s squeek through before that date.