Continuity mistake: In the chapel, before Indy turns the chalkboard over to explain the staff of Ra and the medallion to the G-men, the chalkboard goes back and forth from tilting forward to tilting backward a few times.
Factual error: The interior of the German U-boat is completely different from the real interior of a Type VII U-boat, which is correctly shown in movies like 'Das Boot' or 'U-571'. For example, the ladder from the conning tower faces a different direction, the map table is too big and on the wrong side, the valves for submerging are on the side of the control room and not at its front and stern, depth gauges are too big...etc. All interiors were standardized, so it could not have been an individual build.
Character mistake: When the crew of the German U-boat boards Katanga's ship, the submarine moves in a position perpendicular to the ship's bow as if to block its path. In reality, this would have been a pretty stupid move by the German captain, as Katanga could have rammed the submarine easily. Any kind of damage to the hull, especially ramming damage (even from small ships), would have been catastrophic to the submarine. It makes no sense to make a manoeuvre like this.
Other mistake: When Indy and Marion are sealed in the well of souls, they are completely cut off from the outside world. As such, other than the torches, it should be pitch black, but it is surprisingly well lit in there.
Factual error: There's absolutely no way Sallah and Indy would be able to lift that 'lid' (for lack of a better word) off the ark. That thing is solid rock and would weigh close to a metric ton - and none of them look like professional deadlifters to me.
Factual error: When Indy is attempting to steal the Ark when driving the truck, one of the soldiers shoots him in the arm. Then another German punches him repeatedly in the same arm, causing Indy great pain and injury. After suffering a wound like that there's no way he'd be able to move that arm, let alone raise it above his head. But the next day after the boat is stopped by the sub, Indy jumps into the water and swims to the sub without any problems.
Continuity mistake: When Toht frees Marion, Dietrich enters the tent, and a few seconds later, Gobler does the same. In the next shot, Gobler enters first, and Dietrich second. (01:07:52)
Continuity mistake: When Belloq and the Germans are at the Well of the Souls, a top-down view shot when Indy yells, "Why don't you come on down here and I'll show you!" shows Belloq and a German soldier kneeling down to the left of him, also looking down into the hole. But, the side view shots show only Belloq standing near the opening.
Continuity mistake: When Indy is listening to the one Army agent he is in the process of putting his right hand into his pocket. In the next shot the hand is back on the leather case. (00:16:46)
Continuity mistake: When the Cairo Henchman pulls the knife on Marion, the blade edge changes position from down to up to down again.
Revealing mistake: During the big car chase where Indy follows the ark, he comes down a hill on a horse to get into the truck. You can tell the ground has already been disturbed by the horse from previous takes.
Revealing mistake: After the German is chopped up in the propeller and the plane explodes, you can the blasting cord exploding along the path to the explosion.
Continuity mistake: When Indy sits down in the seat of the plane look behind him, there is nobody holding a Life magazine or fitting the description of the man later shown watching him from the other seat.
Continuity mistake: During the truck chase, as Indy is fighting with the German driver, they knock over some scaffolding and a man drops down in front of the windshield. None of the workers on the scaffolding landed on the truck, much less the front of it. So, he shouldn't have been there.
Continuity mistake: In Indy's class at the beginning, the girl that lowers her eye lids to show the phrase "Love you", is looking in a totally different direction than the people behind her. They're all supposed to be looking at him, but the girls behind her are looking to their right while she is looking straight. They can't be daydreaming because they're all smiling and look infatuated. (00:13:58)
Continuity mistake: When Marcus enters the classroom he leans up against a wall and there are 2 girls in the front row next to him. When the bell rings, the girls are the first two students to leave the classroom. Seconds later when Indy looks over to Marcus the same two girls are just getting up from their desks.
Continuity mistake: Indy and a Nazi soldier are fighting in the cab of the truck when they come to a place where a stone building is being built. As the truck is driving into the scaffolding, several rocks come down and hit the truck and remove the rack from the top. Moments later the rack is back in place. (02:50:00 - 03:01:00)
Continuity mistake: As the big German engages Indy in the fight, Marion is removing the chocks from one of the wheels. In the wide shot you don't see her at all, even climbing the plane to knock out of the pilot.
Other mistake: After Indy shoots the driver of the truck that Marion is supposedly in, the camera looks at the driver's bloody hand falling limp. In the shot of the truck tipping over, you see the stunt driver working the wheel.
Continuity mistake: When Indiana is confronted by the Cairo swordsman, he already has his left shoulder pointing towards his opponent in the shot where the crowd scatters. But in the following shot, where the swordsman is first seen, Indiana has his right shoulder pointing forward and is just turning around to his left side. (00:40:14)
Answer: The scene you describe was indeed filmed. It was cut out of the US release of the film although I cannot speak for the Australian version. The scene also appears in the Marvel Comics adaptation. http://www.theraider.net/films/raiders/deleted_scenes.php has a list of this and the other deleted scenes.
Phil C.