As I understand it the A300 was dealt with first as it is a twin and the control problems associated with a T/R deployment would make it more of a challenge that if the same thing happened with the old diesel 10.
The difference between the 747 and the DC10/A300 has nothing to do with the nacelle, or T/R structure.
The 747 T/R is exactly the same structure as the A300/DC10.
The ACTUAL diffence is the installation of a mechancal throttle interlock on a 747 'build' T/R halves and the installation of a T/R pneumatic limit switch on the engine, which limits the max N1 in reverse.
The mechanical interlock cam is fitted to both T/R halves and releases the throttle mechanical interlock in the same way as the pneumatic interlock on the RHS of the A300/DC10 T/R. This means the eng cant accel in reverse until both sides have deployed, unlike the A300/DC10 which rely on a pneumatic interlock on the RHS only, hence poss acceleration with one side out of position