I originally intended to add doohickeys but instead opted to do the original version and add ICM Soviet Motor rifle troops on top, and do the BTR as depicted in the ICM box art.

New problem: I'm trying to depict a muhajideen firing from up above, but where can I get a suitable figure?

It's probably going to require a good old fashioned kitbash - perhaps Zvezda's 1/35 Soviet Paratroopers in Afghanistan to start. Their arms are molded to accept various Soviet Bloc weapons, and at least two of the poses (prone machine gunner and kneeling soldier) can easily be modified to be firing at a downward angle.
You could blend them with these these figures, based on a few friends of mine:


Hopefully you can get close to what you need.