So I have a '69 12 bolt housing with NO bearing caps. I bought some caps on ebay and have not received them yet. I've read that's it's very important to have the original caps and have them marked. What can I do without the original caps? (The original caps are long gone) Can I still use the ones from ebay? If yes, how do they machine it? If not, what are my options? Thanks.

Jim,
It might be possible to machine the caps to match your housing, sort of like align boring a block with new caps, but to be honest with you ... unless this type of work is a lot less expensive in your area than it it here, you will probably be ahead of the game just finding another housing that is complete. I do beleive that there might be some aftermarket caps available too. They would be easier to install than caps off a different housing, but still not cheap.

So what is the risk of using non-matched bearing caps? It seems to me that the races are pretty thick and won't bend.

But, if the saddles are off, it distorts the outer race. One last resort, you get the caps, install them, torque both bolts to 65 ft./lbs. The round side of either cap goes to the outside, trhe sharp corner side goes towards the ring gear.

Then take a pencil on its side, wipe across the joint to view the amount of lead left.
If no lead, good cap alignment.
If lead is present, swap caps and retry.
If lead is present again, then align bore.