The check ball is a very poor engineering design at best, and the last thing that you need is more restriction in the oil return galley in your rear main with the leak that you currently have. Think about it.........your engine apparently was freshly rebuilt before you purchased the car and whoever did the engine left the check ball out for a purpose. In your case, due to the rear main leak that you have, at this point you should probably leave the ball out until you find the problem. After you get your leak fixed so that you are not oiling the roads any longer, then you can think about putting the ball back in. However, as you know, the ball only is there if you park your car on a very steep hill.....that's the only time that the ball works. The rest of the time it is along for the ride. And, if your rear main doesn't leak then having the check ball in place is cool.
The leak that you have apparently takes a while to develop, which means that the oil is not returning to the pan as fast as the oil is getting to the rear main. Therefore, the longer you drive the car, the larger the oil leak you will probably find when you park your car back in the garage.
Steve told you that the ball belongs there because he doesn't have a massive rear main bearing leak in his car like you do. If he did, I'm sure his opinion would have been different. At any rate, pulling the engine at this point is probably a good idea so that you can better check things out. Also, check the clearances of the rear main oil slinger as well. That might be your problem.
Good luck and I hope that you can correct your oil leak so that you can have fun driving your car.
