The one in Mr Zxp's photo is the one, and only, design for the 77-78 750F. The one the guy is selling as a '78 750F is a 750K cover, he probably just doesn't know that much about his bike. Auction says "78 F K".
The one in the bottom pic is the aftermarket type modeled after the K cover but would fit 75-76 F models as well. There probably was a time that 77-78 covers were available in the aftermarket but that time has long since past.