Welcome here! From the pics and your description, it doesn't sound as if you overpaid. Nice wagons are hard to find. Looks like you've got an excellent base to start with. Tune-up parts and technique suggestions are in
this thread. You may want to do the
Fuel line mod, too, and if the car still has breaker points put an
HEI upgrade on your to-do list.
The engine needs periodic careful
valve adjustment. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download. Get the factory service manual described
here as soon as you can and start reading.
Use a reputable brand of oil -- 10w30 is fine if the engine is in sound condition -- and a good filter (Wix, NAPA Gold, Purolator...not Fram).
I like
Magnecor spark plug wires.
Take a careful look at the engine mounts. The rubber blocks should be square like bricks. If they are bulged, sagged, and/or cracked, replace them. Get the left and right ones
here, and the rear one
here (last item on the page); these are premium items you will never again have to replace.
Once you've got the car in good running condition, Safety is next up, and better seatbelts should be near the top of the list—
even if you're starting with a '70s car that already has shoulder belts. Lap belts make sure the bottom half of you stays put while you're biting the steering column when the car stops suddenly, but that's all they do. The '68-'73 separate shoulder belts are an uncomfortable nuisance to use and can be injurious. The '74-up "unibelts" are easier to use, but still not very good compared to newer belt designs, so it's a very good idea to put in proper seat belts; spend money on seatbelts that are both
new and
good, then hope you never have to get your money's worth out of them.
I used to think it was a good idea to put in 4-point harnesses, like the Wesco setup, but
not any more (the article is correct in its facts and physics, and everything said about 5-point harnesses is equally true of the 4-point variety, except the additional injuries that a 5-point can do to your 'nads).
I recommend
these up-to-date, reputable-brand (Securon) ECE-approved 3-point seat belts. If I needed mounting hardware, I'd be perfectly happy to buy it again
from Wesco (and their page has good illustrated write-ups on how to install belts in pillarless cars
here ), but the Securon belts are a much better-designed product than anything Wesco carries.
(There are also bench- and bucket-seat 3-point belt setups available from other outfits, but I can't recommend them without more than a one-line say-so from the company that their belts actually meet the relevant safety standards; discussion on that matter is
here.)
Another option if you're feeling ambitious: Chrysler Sebring (or other) bucket seats with built-in 3-point belts—info and links
here.
Unless the brakes are newly (or almost newly) redone, I'd put them near the top of the list for upgrade. Three systems were available in '66, and basic equipment was 9" drums at all four corners -- a system only marginally adequate in its day and really inadequate today (especially with those hills in SF!). And regardless of whether your car got the 9" drums, the 10" drums, or the discs, in '66 all the systems had a single-pot master cylinder, really not adequately safe. Ask for advice as a separate thread.
Good shocks (Bilstein or Koni -- buy nice or buy twice!) and good tires (not from China) go without saying.
Of course, being me (the car lighting guy), I would put in
better lights -- there is a mountain of fraudulent/dangerous/illegal junk on the market, but even if you disregard all the junk, there's still a wide range of good, effective, safe, legal
options including good halogens, good LEDs, and good BiXenons for the headlamps along with
relays,
good upgrades for the tail/stop and backup light bulbs, and a
3rd stop light, etc.
After making the car more adequately safe to drive in today's traffic, I'd
then think about turning my attention to more extensive performance upgrades. A
high energy ignition upgrade, perhaps a 2bbl intake and carb (not entirely trivial on a '66 due to throttle linkage configuration, but certainly not impossible, see the
parallel 2bbl setup article -- photo documentation of a very well done such conversion is
here. And a nicer exhaust system with 2¼" headpipe as described
here. Stock manifold is fine if it's not cracked, but
Dutra Duals are better. My opinion and recommendation is to leave the muffler quiet. Loud ones are fun for a week, then they get old in a hurry.
There's an endless amount of money, time, and effort you can put into the car. Do it thoughtfully and one bite at a time, and you'll have lots of fun with a steadily-improving car.