First, the harnesses that Rick and Mike recommended are the same, Factory Fit harnesses made by American Autowire. Excellent stuff, and a good recommendation. I just figured I'd take a minute and expand, to make sure you get what you need.
As you noted, there are two separate harnesses there. Looking at the firewall bulkhead connector, the one closest to the driver side is the forward light harness, and the one on the right is the engine harness. When you look in the catalogs, that is what you will see.
The front light harness contains the wiring for the head and parking lights (imagine that
) as well as the main power feed to the fuse box, the temperature sender lead, and the brake warning light lead; the key in buzzer is also on this harness. The way the main power distribution works in a 1st gen is that power comes from the battery positive to a junction block behind the battery, then via a wire all the way across the front of the rad support to the buss bar on the bottom of the horn relay, and from the buss bar back to the fuse box. The alternator wiring is set up for an externally regulated alternator, and the voltage regulator is mounted near the horn relay on the driver side of the rad support.
The engine harness has the wiring for the starter, ignition (both resistance wire and full 12V at startup wire, so it is setup for factory points ignition), oil pressure sender, wiper and washer, carb solenoid (if you've got one), etc.
The reason I went through all this is because unless the car is being restored stock (gathering from your username I figured there's a chance that might not be what you're after), you may want to change somethings when you order.
If an OE look, with easy installation is what you're after, Factory Fit is still the way to go, and they can easily make some common changes for small fees on top of the "base" price. For example, you can ask for an engine harness setup for HEI/non-points type ignitions, with a single fat 12V feed instead of the OE two wires (resistance wire and a 12V feed when starting lead). You can ask for a front lighting harness that is setup for an internally regulated alternator, so you don't have to have a couple jumper wires added on. Those are the two most common mods, and making them isn't too bad (I'm not current on what AAW charges for the mods, but estimate it's $20 or so per mod on top of the discounted price you get from MuscleRodz or another reseller. I don't know Mike's pricing, but I think he's right on with everyone else and you'd be looking at say under $300 shipped for the two harnesses.
Now, just to throw another thought out there, if you are not going OE restoration on your car, want a lot more circuits and a lot more flexibility to have things common on, say a Pro Street type build, like electric fans, electric fuel pump, etc., you don't mind more labor on your end (don't need "plug and go" convenience), but still want it to look OE, the AAW Classic Update may be a good choice for you. For about $150 more shipped, you get almost every OE circuit thoughout the entire car, front to back (the Update doesn't use the buss bar/horn realy to distribute power, hence the "almost") plus a whole bunch more like power seats, power windows, fuel pump, engine computer, electric fan, etc.). The Nice thing about the Update compared to the lower cost kits like Painelsss, EZWire, etc., is that every factory circuit includes the factory style connection, so...if you take your time, get 3 rolls of non-stick vinyl harness tape, have your beat up OE harness, AIM, and Team Camaro handy during the install, it looks so factory only someone who has done an Update this way or is really anal about factory wiring would notice it's not factory.
If it interests you, do an advanced search on here under my name with the key word "Update". You'll see quite a few posts where I sing the praises, but you should also find a post where I laid out how much time each "chunk" of the wiring project took me.
As a plus, if your dash harness and rear body harnesses are in decent shape, you can sell them for someone doing an original resto for probably half the cost of the Update.