This is straightforward. To prevent scratches, scoop the ring out with a non-metallic tool. Grease the new ring and stretch it a bit with your hand and slip it on the distributor housing. Make sure it doesn't have any kinks or twists.

Install the distributor making sure the tapered end of the key matched the D on the camshaft. You may find there isn't enough room to comfortably install the distributor. But once you do, my main caution is that you DON'T OVERTIGHTEN the distributor bolts or you'll crack its housing and be in dire need of a new one. And they're not cheap.