It's really easy to do, but you should set the timing afterwards. Clean off the bottom of the distributer and the block where it meets it with a rag and some degreaser. Take some whiteout, and mark a line across the bottom of the distributer onto the block in a visible area. The line will help you line the distributer back up when you put it in. Then pull the distributer cap off and just set it up on the intake or something like that. You should be able to do it without even removing the wires. Use the white out again to mark where the rotor is pointing on the edge of the distributer. Unplug the wiring harness to the distributer. There is one 1/2" bolt on the hold down, you have to remove on the hold down and the distributer pulls out. You'll probably have to jiggle it a little. The O-ring is on the bottom the distributer casting. Change the O-ring and clean it out. When you push the distributer back down in, you have to point the rotor to the left of where the mark is, because it will rotate to the right when you push it back in. Line everything up with your marks, and bolt it back down. You should retime the engine after you do this, but if you don't have a timing light, it will be close enough. I find that the white out method gets it real close.
Kurt