If your doing this yourself I would advise drilling a small hole where the notch is going and measuring to the driveshaft to get an exact idea where it is.
I did my own and found that the driveshaft is at a slight angle as it goes rearward, and by angle I mean side to side, not up and down,....it caused me a smal headache but the job would have been easier had I known.
As for movement there shouldn't be any at all unless your u-joint or swingarm bearings are worn out, go with what Sean says on that one, I had to stick a die grinder down inside my swingarm and re-clearance it because my shaft was hitting the notched area due to the above mentioned problem. Mines probably about .015 which is of course too close for comfort.