If you 69 has a olds rear under it I would get rid of it. The olds rear ends are not really a 12 bolt, but a weak 10 bolt with a 12 bolt cover. Parts for them are expensive. My first 70 chevelle came with an Olds rearend under it. I would look for a 12 bolt. You can sell the Olds rearend to someone who is restoring a 442 or and Olds car. Check the numbers and date code and see what it came out of. I personally would run a 3.73 over a 4.10 especially if you plan to drive it on the interstate.
Olds rearend
http://s777.photobucket.com/albums/y...=Olds-Rear.jpg