All the B's have the same design,but there are differences in the main jets, easy to change, and differences in the airbleeds,off idle transition ports and power valve flow, these things are not easy to change.
If you intend to use daul carbs, try to get a pair with the same specifications.
B's often have troublesome fuel leaks,you might try for Carter or Holley single barrels if you aren't dead set on using the Rochesters.
