Sorry to hear that you have had such a problem with the mycobacterium avium complex (MAC) and have been left with some scarring. However, it is very good news that there are no signs of active disease. It might be a good idea to confirm that with culture of either spontaneous or induced sputum. Also, if you have not consulted with a pulmonary or infectious disease specialist, one with a lot of experience with MAC, you definitely should.
I have a couple thoughts about your lung function. First, consideration should be given to the possibility that some of your limited lung function is due to airway obstruction, rather than the restrictive lung disease related to the scarring. If so, the airway obstruction may be at least partially reversible, in response to the administration of a long-acting bronchodilator. Second, your oxygen saturation should be checked at rest, with exertion and while asleep, to determine if you might benefit from supplemental oxygen, at least some of the time. Third, if you are not already engaged in a regular exercise program, I strongly suggest that you initiate such an exercise program. With physical conditioning, even should your lungs not change one bit, you will be able to exercise at a higher level in a more sustained fashion. In order to achieve maximum benefit from the exercise, it may be necessary for you to use supplemental oxygen.
Finally, if you prove to have reversible obstruction to airflow, the kind of thing that is typical for asthma and bronchitis, the Inderal® (propranolol) may have an adverse effect on your lungs, in that it can counter-act the bronchodilator’s effect.