DiabloScott

Looking for some common ground here, my advice was
So if a guy doesn't have the perfect Schrader tube but he has a right-sized Presta tube I suggest he install it and go ride... even without the little knurled nuts with the chamfered shoulder. Be careful with putting the pump head on and off, of course (a little more careful than usual).
It might be fine forever, it might wear out faster than he'd like, but it's not going to be a catastrophe. Also - pack ANOTHER presta tube in your pack for a spare in case something normal will happen like you run over a roofing nail.

Ride now.
Shop later.

1989Pre 

I'm learning along with you, because I bought a Claud Butler yesterday on Craig's List, and I was surprised to find that the rims were 27" Super Champion Gentleman. More-surprising-yet was that the rear rim is schraeder. Velobase says they built them both ways. The tube inside the rear tire is a CST from China, and seems very substantial. Not sure I want to ride with such a heavy tube if I have a tire with puncture protection.

JohnDThompson 

If smog can degrade the exposed base of the stem, what prevents it from degrading the interior of the tube?

Sure. By degrading the organic material it contacts.

The air in your tube is compressed to 7 or 8 bar, which means more ozone than the same volume at 1 bar, and it gets replenished every time you fill your tires.

dddd

The amount of ozone in even one hundred highly-inflated tires is nothing compared to steady exposure of continuously-replenished smoggy air.

As I said, the ozone concentration is quickly lost to any organic material that the air is contained in, leaving simply too low of a (concentration X duration) to have any significant effect.

Once an ozone molecule reacts with whatever it attaches to, it becomes neutralized. So it takes a continuous re-supply to go on to do any significant amount of damage.

Ozone, being a polar molecule, readily attracts to the differing molecular presentations of many kinds of surfaces. As such, a steady stream of polluted air (especially as when riding, or transporting a bike on a car's exterior) will cause the greatest number of ozone molecules to find homes on surfaces that present their own polarities.
Such pairing will cause significant cracking "rot" of butyl and other types of rubber if surfaces are left exposed long enough.

Gum hoods on stored bikes in bad-air areas should be kept at least loosely wrapped as I've noticed that even paper offers significant shielding from ozone's polar molecules.
The air under the paper obviously ends up seeing a lower average concentration of ozone, from either the paper's or the hood's tendency to attract the polar molecules. The rate of attack is thus slowed.

dddd

It's hard for me to imagine such a narrow rim's designer even thinking about blowing that big of a hole through both walls of such a rim, so I'm thinking that it was a concession made to those who were marketing these rims to, shall I say, "stubborn and/or pragmatic Yanks", likely as a marketing-pushed "manufacturing variance" issued some time after these rims were designed.
The discussion probably centered on the pragmatic view that "the consumer is going to drill them anyway".
Some tubes, especially Shraeder tubes, already have difficulty seating their stem reinforcement pad between the beads of tires mounted on such narrow rims. Ruptures (or the tell-tale stretch marks) of the tube just to either side (along the rim) of the reinforced area are common to find on tubes mounted to such narrow rims, as the air pressure alone may not fully seat the valve stem's reinforcement in the rim cavity.

To be sure though, the Gentleman was just a bit wider and stronger than comparable narrow rims made by Mavic and other competitors.

RCMoeur 

Beginning in the 1980s, I owned Super Champion Gentleman and even narrower Rigida rims with Schrader drilling and valves. Although the valve hole occupies a substantial portion of the rim face and the thickened part of the tube can overlap the sidewalls, I never encountered a problem with the valve or valve area, and got good service from the wheels. I think I still own one of the wheels with the Rigida rims.

dddd

Back in the day, I remember those Rigida rims being the most fragile clinchers, which surely wasn't helped by the super-narrow tires that got mounted on them.
You must have been quite conscientious with your inflation psi to avoid flat-spots. Many riders back then initially assumed that they could inflate those narrow tires only weekly or so. But the narrower tires lose pressure faster.

But those same narrow tires actually help with the tube reinforcement area seating in the rim, since the tube doesn't get dragged past such a sharp corner after air pressure has already pinned it to the inside wall of the tire and while the rubber pad is still seating down into the rim cavity. For this reason, I always give the valve stem a tug as I inflate past ten psi when inflating wider tires on the narrowest rims.

Chuck M 

I'm just going to leave this here...