If you can load the Mustang on a dolly, you should be able to load it on a trailer--------and a trailer is the easiest way to move the car one time.
Even if you can tow it 4-down, you will need to figure out a way to hook a hitch to it (probably need to buy a baseplate and install it). Then there is a towbar to buy/borrow as well as hooking up the tail/brake lights.
Just rent a trailer and figure out how to load it. I've backed trailers into a ditch or depression to reduce the loading angle. Or get some 2x12's and some blocks to support the 2x12's at several points along them.
