Flying domestic with big sporting equipment
 

So I need to take my Hang-Glider from San Francisco, CA to Orlando, FL. It is not in pre-approved sporting equipment list for most airlines. Even after doing the "short" pack, it would measure around 12.5' in length and about 3' in width + height. It would weigh around 70lbs.
There are non-stop flights by Southwest, Alaska and United on this route. Airline customer service has provided mix answers, some of which seem too good to be true. E.g. Southwest rep claims, they would allow swapping it for one of the checked bags at no extra cost, while suggesting it is on the discretion of the sw agent at check-in.

Does anyone have experience or vetted information about flying with such luggage?