No external changes...... EXCEPT for one BIG thing: The flexplate/torque coverter or flywheel IS neutral balanced for the '68, but is NOT neutral balanced for the 73'; the late 340's have an offset weight to provide the extra external balance needed for the cast crank in the '73. Which assumes that your motor has the later cast crank in it, and has not been rebalanced for internal balance only..... neither of which it sounds like you know for sure.
