Timing Chain Replacement Question

I have the engine out cleaning everything and replacing the likely parts before I put it back in (water pump, timing chain, etc). When I removed the timing cover I noticed the small gear was lined up perfectly, the large gear was exactly 180 degrees off. Car was running fine when I removed, and I had everything lined up, dist. pointing to #1 and all. So now, what do I do, the large gear will only fit on one way. Do I correct it and if so now what do I do to the Dist, turn it 180degees too? Second question, when I removed the small gear I noticed there was a concave ring around the shaft about where the front of the gear would have been, is there something that goes in there to hold the gear on? Third question, I hadn't thought about replacing the Oil Seal on the chain case cover, should I? By the way, you can probably tell by my questions I'm a fake gear head :read2:
Thanks Bill