as for the jabba scene, I know it was originally shot, But I highly doubt they planned to replace jabba with a creature back in 1976, it was just going to be that guy, and here's why:
1.the guy is in costume
2.Han refers to him as a human being
3.There was no way to technically achieve that shot back then, nor would ILM have any belief they could, its a moving shot with no blue screen and Han walks both infront of and behind Jabba, hell ILM had trouble doing it with digital technology, there is no way they would of shot it the way they did if they intended to sub in a creature afterwards, not in their wildest dreams.
Look at the shot, it would of been impossible.