The undertrim (under your glovebox) would cover the a/c and all the hoses if you had one. I don't have a/c but I've seen the cars with them and it covers all that up. I actually had mine off for years. No reason just never got around to putting it back on.
All the gauges when the car isn't on rest way over to the left. When the car is on and warmed up your temp gauge will move up and over to just past that second line. At least mine does and it's fine. Just know that while you're driving the gas gauge does move one way or the other a little. Kind of annoying but it does it. These are cold blooded cars and must be warmed up before driving. When you start it up let it run for a bit and then tap the gas. If it doesn't idle down it's not warmed up yet. You'll get used to the sound of the engine and know when it's ready.
If you want, I made PDFs of my owner manual and service manual you can download here: http://community.ratsun.net/topic/49640-1981-datsun-210-manual-pdfs/. The owner manual will help you out. Will probably answer some of your questions.
Oh, and I completely forgot, my uncle has made moulds (DUH) so he's looking into a proper resin and I need to get the emblems over to him to look at but I'm on track to make up some new 1/4 panel emblems.