Paul,
I'm a little late in seeing this post, and you've probably planted your trees but here's my thoughts. Our land is flat and the soil is heavy with a lot of clay. We bought some fruit trees during the winter and then had misgivings about how to plant them because generally apples and peaches prefer well drained sandy soils. I found a suggestion somewhere (gardenweb I think) to create "raised beds" to elevate the tree planting depth above the natural soil level. I had several piles of soil on the place from digging a 600' drainage ditch so I decided to use some of it to raise the planting elevation of each tree. I figured on approximately a yard of soil per tree and moved the appropriate amount of soil into a pile. Added some peat and manure as I built the pile and stirred it thoroughly with my FEL bucket. After the dirt was ready I used the FEL to dig up the soil about 6-8" deep where I wanted to plant each tree. I didn't remove this soil, but just broke it up good about 6' x 6' x 6-8". After site preparation I moved my yard of new soil to each place where a tree was to be planted and dumped it over where I'd broken up the ground. My trees didn't have nearly the root ball that you have so I just finished my mound of soil with a shovel and rake to suit the wife and planted the tree in the center with a shovel. After planting I mulched the entire mound with pinestraw. This year 3 apples, 3 peaches, 3 japanese plums, 4 american beech, 1 pawpaw, and 1 cowcumber tree planted using this method. We'll just have to see how they survive the summer!
Another method I tried this winter for transplanting some trees seemed to work mighty well. I put my pallet forks on the FEL and moved both forks together on one side. Then I used the forks as a power spade to dig up the tree to be transplanted. Set the forks at an angle and drove them in underneath the tree from all directions around it. Then "popped it out" with dirt/rootball and transported it via strap/FEL to its new home. Used the same method to dig the hole for it, dropped it in, watered, tamped with down pressure on the forks. All in about 20 minutes for a 10' oak. It's leafed out this spring, but again summer will tell the tale on success.