Hello,
The fighter pull up program is not especially built for mass gain. It mainly focused on strength and endurance. Of course, you will win a little of muscle mass, but only "a few".
If you want to workout out your back, you can add push ups with elevated feet (workout the core) and also dips (upper back) (this one is not "compulsory"). For the abs / back, you can try hanging leg raises (if your shoulders can handle it after pull ups / push ups / dips) or simply leg raises (when you're lying on the floor) or dragon flags.
In all cases, you can use the same progression principle as in the fighter pull up program.
Kind regards,
Pet'