Which axle behind a 502 Big Block???

[NDWEEDS]

So I recently picked up a 1955 second series truck with a 283 in it. The plan is to clip it, notch it and throw in a 502 Big Block! Now I'm not that educated in axles so I need some help here. Im assuming that the 12 bolt and 9" are my most viable options but it seems like the good 12 bolts are a little tough to find and cost a nice chunk of change. The 9" however seems much more readily available and cost a bit less. Am I on the right track here? If I go with a 9", should I have any concerns over strength? What do I need to look for when selecting one of these axles?