A short tailshaft with one shifter mount is for an A body, a longer one is a B body and the dual is a '70 up B/E body. since the E body didn't exist there was no need for the dual mount until 1970, so yes the dual mount with fit any 68' up B or E body though you'd have to modify or replace the 68-69 B body crossmember.
The mount location changed in '70 so the crossmember would be the same for a 4spd or auto I'm told.