Well, just because it "may or may not" have been abused in it's lifetime, don't treat it any differently than any horse who's not been trained at all.
Will you have to spend more time in some areas? Sure, but don't let the horse walk all over you, just because you are afraid to correct bad manners...he is still a horse, and he can still hurt, or kill you, regardless of how he's been treated. Gain his respect, just like you would any other horse.
If you don't know how to get a horse lunging, you may want to get a trainer to work along side you. Lunging is all about body language, and position, and if you've got that down, lunging should be easy to get the horse to do, regardless of whether he "knows" how to or not...it's a bit rocky at first, but if he understands your body language, you should be able to get him going. Maybe try doing some round penning, to solidify your own cueing, but if that still doesn't work, you may need someone who's worked with horses, to help you through the process. Good luck.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."