The C seats on the LAN A340 are much nicer than on the 767. Also 6 across, but since the 340 is wider (8 seats in eco vs. 7 on the 767) the seat is wider and the pitch and recline is also much better.
So if you have a choice between the 340 and the 767 (like on SCL-LIM-LAX) try to go on a day with the 340.