3sp on the floor to 4sp
I am going to do the same swap myself on a 1974 Duster. I have not done it yet nor have I done this swap in the past. But, what I have been told is the biggest items you will need is the 4-Speed Tranny, 4-Speed Mounting Plate, 4-Speed Linkage, and 4-Speed Shifter Handle.
Also, I believe the yoke on the driveshaft may need to be changed to accomodate the 4-Speed.
I hope this helps. Hopefully, somone who has done this swap before will chime in.
Thanks,