Originally Posted by fyerstarter
I certainly think it's possible, but diet will be the most important key.
A year ago I weighed about 195 with 18% bf and now I am 187 with 10% bf so that's a lean mass gain of about 8-10lbs. A lot of this time was spent cutting down too when I wasn't able to take in the extra calories needed to build muscle. Since you are already starting at a low bodyfat then you won't have to worry about that.
I think to gain that kind of mass you will probably need to go through the normal cycle of bulking up to some degree and then cutting down though, it would probably be pretty hard to make those kind of gains while maintaining your low bodyfat the whole time. Then again three years is a pretty long time.
My roomate who is also my training partner is a tall skinny dude, he started out at about 145 a year ago and is now 165 and has not put on any bodyfat at all, just muscle.