Cooling system setup questions for you

[BillyDeluxe]

Hi folks,
I would like to ask some questions about cooling system setup as mine isn't original and maybe therefore not correctly working from time to time.

I have in my 65 C10 Short stepside the following configuration:
- 1980 C10 350 engine (already bored)
- Edelbrock 2601 manifold / 600 carb
- original 1965 C10 Radiator
- stock waterpump
- AC Delco 160F Thermostat
- 16lbs Radiator cap
- additional aftermarket electrical Fan
- 50:50 coolant/water mixture

Problem:
As long as you drive on the highway temperature of engine is down at 160F and everything is fine. As soon as you get stuck and idling in the city searching for a parking space or so temperature is getting higher and the cooling system is not able to bring it down again. Therefore I built in the electrical fan. But nevertheless this didn't solved my problem anyway espacially when it's hot out there. As soon as you get stuck in the traffic after driving a while the engine heats up and starts boiling. Funny thing it that I read an article on a Yahoo! chat which decribes exactly the same problem with the same engine (1980 bored 350). These guys wrote something about thin cylinder walls and much heat generation in the engine.


Yesterday it happened that the Thermostat didn't opened at all. Engine boiled up to 210F before it opened (maybe the thermostat is gone now - I'll change it anyway).

Questions:
- does the Thermostat open because of pressure or temperature?
- do you think the setup is okay or do I need to change something?
- is it possible if the Radiator Cap is the wrong one that it prevents the system of working correctly?
- is the 160F thermostat okay from your point of view? (when I bought the truck from Arkansas it has a 195F thermostat which I changed because it doesn't fit to the German weather where I life)
- Anyone with similar problems? Your thoughts?
- ...

I would really appreciate to get your help on this because I try to fix this problem sinc 3 years now and I have no clou what could be wrong. Maybe someone of you can help.

Thanks guys, Andreas (Nuremberg, Germany)