With a POD not earlier than 1971 (foundation of LucasFilm) let the Walt Disney Company be absorbed by LucasFilm or Marvel until the year 2013.
I'd rather see them being taken over by Warner Brothers. It would make for interesting editorial cartoons. I can see Mickey being led to the guillotine with Daffy Duck waiting to pull the string.
In both cases Disney needs to be badly mismanaged and/or fund a few doomed projects. Maybe releasing the Disney Sequels in theatres will get things going.
As for Lucasfilm Buying Disney, maybe have it less to do with Lucas Exclusively. Maybe Peter Jackson goes to Lucas to make the LOTR trilogy would be a good start, or something along thoose lines.
As for Marvel comics, have Super hero movies be taken seriously earlier on, and eventually have an entire seperate section of Marvel, Marvel Film, that makes movies other than just super hero movies. If the Hypothetical Marvel Film is strong enough it could produce a company strong enough to buy a weakened Disney Hypothetically.