For that high of a ratio, perhaps an OD would be the best answer to keep everything else standard.

Otherwise, Currie makes great 9" rear ends with lots of ratios and lockers. Standard axles are 5 on 5.5" (early Ford, Jeep, etc.) but I bet it would be easy to get 6 on 5.5" axles from Moser or Currie.

Ed Pruss
Longmont, CO