I think you would be fine since you are using a tree spade. I was at University of Houston in the '90's when they transplanted some big 14" live oaks that were 40' tall and they lived fine. Came in the tree spade that dug them out. Remember that most of the root system goes out to the drip line so a crown thinning may be needed to reduce water loss, and a drip irrigation system will go a long ways to helping them through the shock. You may want to check with the people on the Forestry Forum or Arboristsite.com since a lot of them work with trees as a living.
