One bearing is pressed in (rear), the other (outer)is not.

If the car has over 200,000 miles on the original bearings I wouldn't feel bad about replacing them.

I'm curious about a few other things on your car.
What is your rear axle ratio and tire size?
What is your typical cruising speed on your commute?
Do you have a lot of hilly terrain?

With such abysmal fuel economy I can't help but wonder if there are multiple causes, and driving conditions are one. So are high average RPM's.

Fuel economy drops above 65 MPH in my experience with my sedan. If your wagon still has it's 4:56 rear end you would need some pretty tall tires to be able to cruise economically at a steady 65 MPH

The best mileage I ever recorded on my sedan (B20 with HS6's) was 31 MPG, and I achieved that by never, ever going faster than 65. On the same route, going around 70-80 for just a short while knocked 5-6 MPG of my fuel mileage. By the same token, fitting an overdrive to the same car and keeping the speed at 65 (with the 4:10 rear) gave an astounding 35 MPG during a level part of the route.

I've always used premium unleaded.

The wagon is a few hundred pounds heavier than the coupe, so I wouldn't expect results as good as what I got, but you should should still be able to get into the mid to high twenties under ideal driving conditions.

If the carbs and/or ignition system are off (or worn engine), and driving conditions are not ideal, in terms of road speed, terrain, average RPM's and driving style, then I would expect mediocre economy, although 16 MPG is really, really bad for a car that otherwise performs well (I assume).

Was the free play on your master cylinder set correctly?

What's does your engine vacuum measure?

I'm really sympathetic towards your quest for good economy; that is one of my goals for my wagon that I'm working towards (maximum operating efficiency).

I will be pulling out the entire rear seat, replacing the spare tire hatch with a reinforced aluminum panel and the inner tailgate cover with a piece of ABS.

The spare tire will go where the rear seat used to be, to reduce as much weight as possible behind the rear axle, and possibly be replaced with a modern temporary spare if the weight savings is significant.

The heavy trailer hitch that I never use will also come off.

I'm even considering a set of Superlite wheels, since it appears they would knock off about 28 pounds of weight compared to the widened factory wheels I was going to install on the car.

A O2 (UEGO) gauge is definitely in the cards for the future, and possibly a GPH meter as well.

Good luck!

Bill