If you are absolutely certain it's vacant, go for it. But try not to disturb the roots too much. Dig at least a 4ft circular trench around the tree. Carefully dig under it to a depth of at least 2ft. (before you start this, Water the tree - say 10-20 gallons, and dig the new hole you want to put it into - at least 3 ft sq or dia, and water the hole too)
Keep as many of the fibrous roots attached as you can - these are the feeder roots. get the tree out and put it straight in the new hole. Fiil the hole, tread down carefully as you go to get the soil in contact with the roots.
Water it at least once a week.
Best of luck - it can be done.