Which 3rd member is correct for my car?

Hello guys I'm needing some help with my rearend. I have a 1967 fastback formula S 383 auto. My 3rd member is bad and I need to replace it. It has a 489 housing which I know is wrong. My question is which housing and size yoke am I supposed to have? My driveshaft is the small yoke. Has it been changed? Did automatics use the samll yoke? 741 or 742 housing?
Adam
440-258-3009