Digging around a tree for hours at a time is dangerous. You are loosening the roots and taking away the trees support. The wind could blow it down on top of you. That 70' tree would make a huge dent in the FOPS.
I have had operators with decades of experience take down trees that size with 20 ton and larger excavators. They do it in a scoop or three and can control the tree. Even they are reluctant to attack a tree their machine will not pick up.
Why not cut the trees with a chainsaw at shoulder height then dig up the roots and push the stump over with the FEL?
I was trying to use the momentum of the tree to popup the rootball as just digging half of it took about 3 hours. Ended up cutting it with a chain saw as it only came half down and hung up in another tree. Ended up taking many hours to get the rootball out. It was almost the size of the tractor and far to heavy for the tractor to lift. Had to cut the stump right off and chain to an upper root and roll it out. Just to pull it on the driveway would only happen with the front bucket full and backhoe bucket full and fully extended.