I recall a few 727-100's that would have quite a surprising roll on liftoff
That is a result of improper shimming of the flaps. I have personal experience of only one operator checking this and it took 3-4 test flights to correct. The O/B flap shim would be checked at lower speeds clean and the I/B flaps at higher speeds, we had charts with calculations for this it was a scientific process. Now on liftoff with flaps extended a bit this would have effect as one O/B flap could be producing more lift than the other.