In your 6th pic from the top, the antenna holder screws in near the inside rear most corner of the servo. I have discovered though some hard looking at mine that the chassis plate has a "preferred" top and bottom. Won't say correct, but preferred. This antenna holder made that evident. You've put yours together just like I did which has the preferred top facing down, not up.

The holes for the antenna holder are much much easier to thread from the preferred top side, they are chamfered and the holder threads in easy like its supposed to. There's also another place you can put the ant holder toward the rear. I threaded mine in, but it took some real doing using a small phillips as someone suggested. Before I did that, I tried it from other side - threads in so easy its obvious that should have been the top - should have assembled with chassis plate flipped over. Thats real dumb on flm's part not to point this out (its also typical), assuming you want to use their antenna holder...

Thanks for clearing up what the other 2 alum pieces were! I didn't have any clue there.

What motor is that you're running, you're light years ahead of me, and looking at how yours is turning out has me anxious to get mine finished! Yours is looking good! I've got a 8XL, Quark 125 and plan on running 18 cells to get started - reason I didn't use mm. The wiring is going to be a real challenge! Hope yours checks out great, be sure to let us know!