The shape of your AR hammer looks amazingly similar to mine, only I mounted my gripstick up higher - and that's where my 'tight fit problems' occurred (cocking). Congrats on your FP strikes - it is a BIG DEAL! The further you progress, the clearer it all snaps into focus. It's mostly logic.
Question - is the bottom of your TC/feed lever parallel (lengthwise) to your rails? It may be just the angle the pics were taken - be sure the feed STUD engages the feed LEVER (track) during it's entire stroke. You can tell by looking in the rear. I have to remove the stud to slip my BC out. I didn't understand what the square notch in SS's was for, until I was past that point. duh
Robert sells G3 stock sets for $8 HK G3 Surplus Green Stock Set you can epoxy to fit & their spring recess hole is perfectly located for this build