Take a look here:
http://www.bikeaccess.net/bikeaccess/
You may have a problem unboxed if the bus makes stops. Luggage will take priority over a unboxed bike and for that long of a trip you may be looking into some damage. This is from their site;
Greyhound baggage restrictions:- One (1) piece of baggage is checked free of charge for adults and children. One (1) additional piece of baggage may be checked for a charge of $10.00 for adults only. Baggage carried beyond two (2) pieces will be charged based on Greyhound Package Express rates. One (1) small bag up to 25 pounds can be taken on board for each adult or child. Carry-on bags must fit in the overhead compartment or under your seat.
- The maximum allowable weight for checked baggage is 50 pounds per individual piece of baggage. A charge of $30 - $40 (depending on the distance traveled) will be charged for any baggage above the 50 pound limit.
- Baggage must not exceed 62 inches when adding the total exterior dimensions of the piece (length + width + height). A charge of $30 - $40 (depending on the distance traveled) will be applied to any baggage above the 62-inch limit.
- Packaging exceptions will only be made for the following items: bicycles, skis and ski poles must be packed in wood, canvas or other substantial container, and securely fastened; towing equipment must be enclosed in rigid containers or wrapped in a strong material such as canvas and securely strapped or tied. Towing equipment is limited to 100 pounds actual weight. These items are not exempt from oversize charges.
- If bags exceed maximum size and/or weight, customers must ship the item via Greyhound Package Express.