Actually, don't worry too much about side-to-side play on the big end bearing, worry more about the play as you "rock" the rod. The distinction is critical, as it can mean the difference in a running bike and not running, and if you spend a lot of money for nothing.
Grab the rod at the top where the wrist pin bearing is inserted. While holding the rod as straight up and down as possible, try and pull the top of the rod down towards the water pump, and then down towards the other side of the motor. While you should have a little play just to compensate for heat expansion, you shouldn't have a lot.
A good way to measure the play is by sitting a trisquare on the base gasket surface where the cases split so that the ruler is standing parallel to the rod like a knife edge, in the center of the top of the rod. Watch as you try and pull the rod downward, noting the amount of movement. (I hope I have explained this well enough to make sense. If not, just let me know and I'll try again) If you have about 1/8 inch, you should be OK. Any more, you might want to think about installing a rod kit.
Let us know what you find out. Good Luck
Rick