Star Wars was at least partially the result of George Lucas not being able to obtain the rights to Flash Gordon. For the moment let's say George Lucas did receive the rights to make his version of Flash Gordon. Production starts around when production on Star Wars did. What might that film look like? What might the plot be? I know very little about Flash Gordon. Who would Lucas cast? How would the film do? How would Lucas' version compare with the actual Flash Gordon film that was made in the eighties?
The opening credits would be identical to Star Wars since they are 100% copied from the classic Flash Gordon serials of the 1930's.
George Lucas is a terrible director and an even worse script writer so it all depends on whether someone other than George is involved in the creative process.
Flash would be played by wait...............
Arnold Schwarzenegger with a dubbed voice. They dubbed voices more in those days and I doubt Arnold would have cared in 1975/76.
Ming the Merciless would be
Christopher Lee since he had already played Fu Manchu in a movie and Christopher Lee says yes to almost any film role offered.
Dale Arden could be done by
Carrie Fisher
Doctor Zarkov could be done by
Alec Guiness
Prince Baron is more difficult. Maybe not an American since they usually give royal roles to British actors (OTL Timothy Dalton). I think
Michael York.
The Hawk man could be still be
Brian Blessed as OTL.
Mings daughter would have to be 'exotic' looking. So maybe
Barbara Bach.
The climax of the movie would be an attack on Mings fortified palace and would look similar to the X wing attack on the Death Star. Not sure if Lucas would have introduced the force but I am sure he would have got Light sabres in there somehow.
It would do well at the box office but there would be no legend.