For your situation you would have to look at the options of a cargo van rental, or renting a large truck. This would really depend on whether you needed to keep the grandfather clock upright or if you were able to move it laying down.
A cargo van rental would give you the length you require (avg cargo van has 10' interior length) if you were able to lay the clock down horizontally.
If you wished to keep the clock upright, the only vehicle with a 7' interior height clearance would be a 24' long moving truck.
If you are looking to drop off the moving vehicle in Georgia, as opposed to bringing it back to Illinois, you will probably find availability more limited for the cargo van for a one way rental vs renting a larger moving truck for a one way rental. It is very, very rare for companies to offer one way cargo vans... I've never seen that option available.
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