If the back of that is straight.. it is deformed, not bent.
This area/damage is a place you should check on EVERY CB 750. Crash bars and Highway pegs were mounted here, because they were not made well, those bits tend to crush the frame..
Remember when buying one with bars on, that you may have damage there when removing those parts.. if you can see it with them on, use it as a bargaining point to drive price down...