One of my all time favorite lecturers is Lew Farber. At the Vintage Trailer Academy, Lew barked out Yes's and No's to questions like I've never seen. No meandering pre-qualifying, no "It Depends", No conditions.. Just concise strait answers. so...
Land Yachts were Ash. (1st page, right column of attachment)
The most common and advertised International upgrade was Walnut. Back then it was possible, but rare to specify Mahogany or Cherry as a custom upgrade. There is a light coating of clear lacquer as the finish. The lacquer can be rubbed off with your favorite carcinogen, and refinished.
The Single axle 67/68 is a pretty fine go anywhere trailer. Very robust, also very repairable. As your "cleaning" gets deeper and becomes repair and re-configuring, You'll appreciate the simplicity and access not found in today's models. These "Old Betties" are smarter than what's offered today in many ways.
Another great asset of the 67/68 is the remarkably sensible bath. Your black tank is only 18 gallons (I've measured). It's not terribly difficult to remove. Some were polyethylene and some were ABS, maybe California v Ohio, I don't know why. Either way, it can be repaired.
With a Thetford to Valterra adapter and an additional Valterra gate, your black tank will hold your grey water too. This works just fine for a water conserving couple over a week-end. When you remove your black tank you will find that there is room in the next forward frame bay for a grey tank if you want to further your waste water project.
wiring is just plain stupid. Maybe the worst ever of any Airstream. It isn't necessarily dangerous, but re-configuring and updating should be a priority. Try not to be infatuated with the "Central Control". It's actually a dysfunctional, heavy, obsolete, counter space wasting, superfluous, gratuitous, piece of junk. It was the first year attempt at "Central Control", and I can't say if Airstream ever got the subsequent years right. If you're doing a museum quality restoration, you'll have to keep it, but there is nothing in there worthy to an updated electrical system, and keeping it for its "cool looks" creates unnecessary work-arounds...
Yup, the old furnace can kill you. It's too old to trust, and there may have been recalls. Maybe you can find a place for a Marine Bulkhead Heater. Haven't heard any complaints about them in an Airstream. They function safely and are cute.
With wind-driven rain, some of your windows will probably always leak a little into the sill, even with new gaskets. That's just the way the 66-68 windows are... They're easy to re-gasket and DO put fresh tape in the clamp bars, otherwise the glass can fall out unexpectedly...
I've been crawling over and through my 1968GT for six years. I have some pertinent posts, but no ongoing restoration thread. Most of my thread start headings are specific...
Most all the late sixties contributors are well versed. Pretty much, everything you need to know has been published to Airforums.
'68 is an Easy to Love Airstream.