congratulations.
You are doing a great thing by helping out a troubled bird. Just remember to give it plenty of time and patience. My girlfriend adopted a troubled gray, and after 2 years of triying to normalize it, the bird still wont let them take it out of the cage. But he is entertaining because he knows alot of curse words and funny sounds.
Keep at it and don't give up!!!
My Simon was an abused bird that i had saved, he was also a really bad bitter, just couldn't trust anyone. I just kept at it every day, letting him out giving him treats tons of toys and trying to play games with him. Got bit about a billion times. One day he just turned around and was a peach. Now he rolls over and lets me pet his belly. Since he is so tame now, he gets to stay out of his cage all day (if im home). Ive had him for about a year now (he was 6 months when i got him). It took him 4 months to calm down and trust me. We are now working on him trusting strangers. So far so good.
So have faith that there is good in every bird