I operate the A330, as I dont think anyone of us trully flies an Airbus. Have experience on A320 and A330 (and B757), there are some differences but not enough to get concerned about.
If you want to train on a MCDU from a A320, will put you well ahead of the pack for a A340 course, as the whole setup is quite different to a Boeing FMC.
Hope this helps, good luck
