Go on rock auto and get gm or ac delco o-rings, and use them with the aluminum elbows. I did that and about half a year later no signs of leaks.
And just be gentle, that's a very good point on the timing cover Bill, it never crossed my mind!
I just spread a tiny dab of oil on the rings before I slide the elbows in, that way they slide in with very little effort and you can even feel when they're seated correctly. I'm still sticking with the aluminums, they've saved me so much trouble.