The original Chrysler bakelite/phenolic heater valves were junk. The would last maybe 2 years at best before they cracked and started leaking. I have a bunch of them but I won't use them because one never knows when they will crack and start leaking until one notices the engine temperatures start climbing due to leaking coolant. But in the case of the early 70s Chryslers, they only had hot lamps to let you know your engine just got fried because of one of those pieces of junk started leaking while driving down the road. I like to keep my cars usually as much nos stuff as possible, but that won't happen with those crap valves.
The aftermarket has supplied non-original metal heater valves for a very long time and I have yet to need to replace one. They do not, however, modulate the temperature as smoothly as the original ones did.
I have to wonder how many customers never bought another Chrysler product after being stranded on the side of the road a couple times with the original valves. Yeah, they saved a lot of money for the Corporation but they lost so many customers as a result. That's OK though, because the manager of the department got promoted due to his ability to cut costs and went on to his next assignment to continue to lead the company into bankruptcy by 1980.
How are you able to run Imperial mufflers - those were really long and with a large circumference as well and worked well to quell exhaust noise? I haven't been able to find any mufflers in the aftermarket for decades that were as long and effective in muting sound like those did especially when used in conjunction with resonators positioned near the end of the exhaust pipe(s). Like you, I want my cars quiet and do not like to hear the drone of the exhaust hour after hour of driving.
