Another factor to bear on the ferry versus extra pod option is that in the early days of the introduction of wide bodied aircraft ( early '70s) there were very few freight aircraft around which could physically carry complete large fan engines. When Court Line introduced their Tristars I believe they also acquired a Blackburn Beverley to cater for this possibility.
I believe later that some large fan engines could be transported by removing the fan and loading the two engine components as separate units.