Drive shaft for the big auto to 4 speed swap?

Pretty sure your right about that.

Drive shaft lengths are the same from dart to dart, and dusters to demons, dart sports.

The Yoke may be the same as well, just depends on the spline count. I tried to get a Drive shaft lenth altered and they shaft has some rubbber in it makeing it a pain to alter over a certain length. at least that is what I was told from the Fab shop that had my drive shaft. I was trying to alter it for a BB conversion though....You should be A OK!