Ryan McAvoy said:

I always thought the OT was pretty timeless, it was concieved that way.

I don't think timelessness is an easy thing to plan. Sure, you can avoid references to pop culture (use a classical score, don't play the Bee Gees in the cantina), but some things fall in and out of fashion that are hard to control for.

You've got two main characters who are robots. Not little background utility robots, but central characters. And neither of them has superhuman strength or any sort of built-in weaponry. Clearly this film predates the nineties.

The movie is called Star Wars, but it takes about an hour for them to get off the planet and actually into the stars where said wars are happening. Films stopped meandering this much by the eighties.

The color hasn't been manipulated very much at all. The sky doesn't look very green, Luke doesn't look very orange. Clearly this movie was made before The King's Speech.

The film takes place in roughly chronological order. Postmodernism hadn't had a huge impact on film quite yet.

The above are all things I like about Star Wars. Just because they date the film doesn't mean that they are bad. It's a representative 70's film, IMO. And it's great.

EDIT: Good call on Raiders, Bingo. That's probably the closest we're going to get.