Hehe, you know I love hearing about your DS, it is the ultimate, most powerful and fastest D ever, not cheap in any market and thus rare even in Europe. I am surprised that anyone forking out that much for a car didn't want the a/c in a hot climate; perhaps they lived on the coast and never went inland.
Many years ago a friend of mine had a nice '71 DS21 daily driver. It was an early '71 and didn't get the fender vent a/c though he said the original front bumper did have the vents, presumably Coolaire hadn't gotten the condensers into production when the car arrived in Texas. The owner was an engineer and long-time DS guy, but did not like being hot. He kept the radiator mounted condenser but added a second electric fan in front of it, used in conjunction with the factory electric and mechanical fans behind the radiator. Since pancake fan motors were rare then he used a normal 12v motor and had to modify the shroud and relocate the spare tire to the rear. A bit Rube Goldberg, but it worked and kept him cool in Dallas traffic for many, many years.
I've always wondered if both the D and SM would benefit from some small vents in the front fenders to let air out. The SM does not appear to have any more air exits than the D, but the twin fans move a lot of air, particularly the '73 fans with the big motors. I'm not sure if those were installed across the board for '73 or only on three liter cars. One funny factoid about the SM is that there is a hydraulically operated switch to turn off the fans once you hit 30 mph or so when there is enough airflow to make them redundant. It is operated by a high pressure line from the steering speed governor on the nose of the gearbox.
At least with no a/c you don't have to worry about premature timing chain wear from the compressor. Modern Sankyo-Sanden types aren't too bad, but the York type universally fitted in the US or OEM Italian York clone on the SM have high cyclical loads that the timing chains don't like. The D is significantly less sensitive to this than the SM however.
