Generally, a Zero-G parabola is fun to do, but not easy to do precisely without practice. It is more challenging to do with a non-aerobatic airplane like your -9A, because you have pitch limits to observe as to not go into the aerobatics regime - 30 degrees up or down. You also have a fairly narrow range of speed between maneuvering and stall, or in the case of “flaps down”, the top of the white arc and stall. This means you’ll only have a few seconds to establish and hold Zero-G and push the button. (The parabola is much easier to fly in something like a KC-135 because the entry and exit speeds are much farther apart on the ASI, and you can get 30 seconds of zero-G….)
The parabola is a wings-level maneuver, so you only have to dive to the max speed you can get, then pull up at about 2 G’s to the maximum pitch you can use (45 degrees works well for aerobatics, but 30 is the non-aerobatic limit), then push over to establish Zero-G. Make sure you are at Zero with you tennis ball - all the dust flying up off the floor might mean you’ve gone negative - and push the button, then recover before you get too nose low, indicated by pitch or by airspeed getting too high. This can be REALLY challenging with flaps down because the top of the white arc comes up real fast when the nose is low!
There is an ideal power setting to use as well if you want perfect unaccelerated Zero-G flight, but you’re going to be so busy, and the time is so short, don’t worry too much about it. Just don’t overspeed the prop on the down line if you’re fixed pitch. You want has much energy as you can get just before pushing over - time at Zero-G is directly proportional to entry speed.
Sound complicated? Find someone with aerobatic experience to do this with you (or for you) the first few times. Of course, in a -9A, you aren’t going to be doing “legal” aerobatics, so you don’t need a ‘chute for each person on board….
Paul