So the snail won the drag race...

Dave145 said
Where I'm from (southern Wisconsin), my car is emission exempt.

Then if you wish, delete the cat (meow!).

I've recently replaced the thermostat with a 180° one for the summertime. Sure the car runs cooler, but it definitely ran a lot better with the oem 195° stat in.

Put the 195° stat back in.

I'll try and get a feeler gauge and someone with experience to show me around on there to adjust the valves at some point.

Step by step guide at valve adjustment article.

Most common jets to run

Highly variable carb-by-carb.

most common amount of timing

Goal is to get the distributor set up such that you have 5 to 7 degrees BTDC base timing.

Anything else I should be looking for here?

Well, again, you're going to want to check your cam timing. Probably not much timing chain slop with that low mileage, but it's very easy to check (pop off the distributor cap and rotate the engine by hand with the fan and fan belt in one direction til the rotor starts turning, then the other direction til the rotor starts turning; you want minimal/zero delay between turning the engine the second direction and the rotor beginning to turn).

What mpg numbers SHOULD I be seeing from this car?

In perfect tune, a dead-stock '76 Slant-6 Dart driven conservatively at sea level will return about 15 city/20 highway.