Jacko, there is absolutely no chance of a 'A300 with an A330 cockpit'! A while ago, a full-glass cockpit was proposed, but there really isn't any need as the 'half-glass' is good enough for the purpose.
A 'short' A330 is not needed. Neither is any commonality with the A330 needed.
Another good reason to use an A300B4 freighter is that fitting any temporary 'mission equipment' is a lot easier with a cargo door. Plus, unlike the 767, it has a true wide-body fuselage with the same cross-section as the A330.