American cars peaked in the middle 1960's for your argument, LarryL. A midsize car, with smallblock V8, AC (if down south) would run about forever. If we could bring it forward in time, add electronic ignition, radial tires, modern brake pads/shoes, gas-charged shocks and a GEAR VENDORS overdrive we'd have the problem covered.
I'd still upgrade the electrical system, but that's about it.
Oh, yeah, three-point shoulder belts, not the pair of belts each position had.
Here's a nice example of a 1967 DODGE Coronet Coupe:
http://www.cardomain.com/ride/339919
The Big Four automakers were still advancing in engineering terms (it came to about an end at this point), reliability was way up over the early 1960's, and many of the components developed then were in production until only a few years ago.
Nothing complicated. Needed good attention about once yearly per fluid changes/tune-up. A carb overhaul at about 50,000.
We could rustproof, use a stainless exhaust, etc, but that is primarily cosmetic.
Weight, size, ride, etc, were all to the good. It's been downhill since then.
I don't daydream about todays cars . . just the bucks to completely rebuild an old one (as I was doing until health went kaput). For the price of a very nice new car, I could commission a rebuild of an old car that would do another 30-40 years barring major accidents and fires/theft.
With a 318-V8 done properly, 22 mpg highway is not out of order. I was getting 17-19 out of my 383-V8 4,700-lb Chrysler. This car would come in about 1,000 lbs lighter.
When I think of all the fine old cars that were run into the ground . . the waste of capital, labor and resources to build new ones constantly makes no sense. We could have a few million older ones providing good service had we, as a society, elected to train young men/women to restore and maintain these cars. There is certainly no lack of folks who could use one.