25.5" wide x 33" deep x 73.5" high. The Explorer should be big enough. Bring help - it's a heavy, awkward machine.
Make sure the PCBs, ARII, monitor, coin vault and power brick are all secured properly before you put it on it's side or back. I had a Tempest I transported once that had the power brick just sitting in the bottom, and it tossed around quite a bit while moving it, but thankfully everything survived. I also moved a Millipede where the coin vault was not attached properly, came off, and did the same thing. Got lucky with no damage on that one, too.
Good luck.