Power Steering Pump Overflow

I'm putting together a non-running (at least since I got it) '66 Barracuda 273 2bbl. It came with power steering. I 'primed' the system by adding power steering fluid while slowly working the wheels back & forth (wheels off of the ground). I stopped adding fluid when it got to the bottom of the neck of the pump. The dipstick shows fluid just below the 'add cold' level on the dipstick. I tightened the cap/dipstick & turned the wheels back & forth & fluid overflowed over the top of the neck of the pump - as if it was overfilled & I don't know why. The cap looks to be in good shape....nearly new in appearance, screws on nicely, and says 'vented' on the top, but I can't see where/how the air would be able to escape. Actually I don't know for sure if it is the right cap...or the right pump. I've never messed with power steering before, so I don't know what I'm doing wrong. Here's a couple of pictures of the pump, & the cap. Are they correct? I'm hoping I'm just doing something wrong. It wouldn't be the first time. :( Anyone?

Power steering pump 1.jpg

Power steerein cap dipstick.jpg

Power steering cap vented.jpg