Mustang 1973 Power Steering fluid?
You are absolutely right. That type of Ford power steering pump was a round canister with a tube sticking up out of the back and used the short dipstick as the way to check it. And it DOES NOT say power steering fluid on it. It is just a little curved handle that looks like your oil and transmission dipsticks. And the stick itself may or may not have a grid or a bunch of X looking marks on it, but either way, it will have the C and H marks. And as you probably already know, that is your oil level marks, depending on whether the engine is cold or hot. On that type of power steering canister, pour the fluid in very slowly and not much at a time. While you are in the process of doing that, check the level fairly often. It is VERY EASY to overfill those type if you aren't careful. I was so glad when Ford started using the GM style resovoirs. You could at least see down in them to see how much you were getting in them. And yes, ATF will work fine for p/s fluid. Any good Dexron/Mercon fluid.