300SD and 190SL

Even though I have been a MB owner for over
18 years, I recently found your site: GREAT!
I have a 1984 300SD and a 1963 190SL.
SD Questions:
1. What should the oil pressure be after
traveling on a long trip on the inter-
state going 75 mph. (car has 221,000
miles). Really, want to know what would
be normal with this mileage.
2. This year when I turn on the air
conditioner, the car will idle great
for maybe 5 seconds, then it will begin
to idle rough. Other times, it will
idle rough all the time with the air on.
Previous years, idle was the same with
or w/o air. Car idles as a gasoline
car with air OFF. Cools great!
190SL Question:
Car has webers with the "pancake"filters.
Will installing the original silencer
make the car sound much less nosiy?

I realize this a long post. Answer only if
time permits.....THANKS!!