You could install a manual shut-off valve. Many have done so in many U.S. cars, indeed I recall photos and PN's on a Mopar site I frequent (forabodiesonly.com). Your heater hoses are std 5/8"D, at least that is what I used when I removed the "aux water pump". I used silicone hoses which stretches more to fit the unequal sides.
I am dealing w/ a similar "too hot" issue in my 1985 300D. On the "max cool" click setting, I also get AC fine. That tells me that my monovalve works fine (your too presumably) and the problem is in the control loop. I measured the resistance to ground at the temp sensor input wire to the TemperaturRegular box (above glove-box) and found it open. I installed another sensor (behind push-button box, to left of fiber spider) from junkyard, but still "too hot". It read ~12 kohm at room temp and dropped to 8 kohm blowing on it, which is about right. But, the old one checked out too (recall it showed open when I tested it alone prior), so problem might be in my wiring. Anyway, gives you ideas how to proceed. It isn't at the top of my current priorities.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans