I'm (trying) to replace a ceiling light fixture in my son's bedroom with a fan/light fixture. The old ceiling light ran off the wall switch, and I'd like to keep it that way (my son is only 4 and can't reach the pull chains). The problem is, our house was built in about 1950, so the house wiring doesn't follow the modern standard color coding.

In the ceiling box, there are 4 wires: 2 brown, 1 ivory/white, 1 red/white stripe. One of the browns is off to the side, and the other is paired with the ivory.

Here's the layout on how the old fixture was wired in:
brown, brown, ivory to fixture black
red to fixture white
fixture bare copper ground unattached

Since the red was connected to the fixture white, I'm 99% sure that the red wire is common. No problem there. My confusion is how to hook up the two browns and the ivory to the new fan/light fixture.

On the new fixture, here's what I need to do:
(hot) to fixture black
(hot) to fixture blue
red (common) to fixture white

So I have three potentially hot wires (brown, brown, ivory) coming from the ceiling, but only two connections to make. How the heck do I tell which ceiling wires to hook to which fixture wires? Can I do it without a meter?

Thanks in advance!

(As you can probably tell, I'm new at this. Simpler explanations are better.)