I have two questions. What are folks doing for these? I’m doing the chins & plain planks. Thinking about mixing up the planks. I like the chins.
Anybody adding anything? I was thinking about throwing in a submaximal 8 minute AMRAP of push ups to aid my upper body volume.
for “upper back work” my default is chins. Although sometimes i’ll do T-bar rows, if available, or pendlay rows.
for “arms”, I’ve been known to superset curls and some tricep movement like LTE’s or push downs.
for “abs”, I’ve been trying to work on my strict toes to bar. I have done ab wheel rollouts, L-sits or try to get from an lsit to an handstand on parallellettes. That one is fun. 
I use an elliptical for the LISS & HIIT, for upper back I do pulldowns and cable rows, and for abs I do planks, crunches, and reverse crunches. I save barbell pendlay rows as an option after squatting.
I’d probably stay away from push ups on GPP days and stick to vertical or hortizonal pulling
So, if I have an “imbalance” the suggestion here is that needs to be addressed in the lifting days with more volume on those movements.
The “suggestion here” at BBM is that imbalances don’t exist, as @Dave_Hahn explained above.
As for GPP,
Pull ups, as many as I can get in in the 7 min allotted,
Abbs, I do various forms of planks, then rotate between planks and certain holds where my feet are in the air and I’m either on my shoulders (“Dragon Flag”) or ass such as V-sits. All isometric holds.
Arm Work: I do my version of the arm work advice given in Jordan’s 12 ways to skin the TM:
1 bicep exercise and 1 tricep exercise, do 8-15 reps per exercise and alternate back and forth until your arms fall off. The idea would be to increase the volume over weeks, i.e. add more time to the training in order to accrue more reps and sets.
For me, I pick a moderate weight for Hammer Curls and overhead tri. extensions, and do sets of ten alternating with no rest until I can’t do another set, or the 7 min are up (hasn’t happened yet in the 2x I’ve done it with the bridge)
Interesting regarding alternating the biceps/triceps. Where did you see that? Going to start doing that.
Since my bench has started moving well on the Hypertrophy program I have decided against the push ups and added presses instead. I do submaximal sets of five for 8 minutes after the pull ups. I’ve only been doing it for a week so who knows if it will help my woeful press or not. Maybe there’s a visible difference? Feels like it, who knows.