Unless some changes have been made, no 1800 came with an "A" series engine. A means single carb with an A cam. 1800S with a B20 should have a B20 B with a C cam. If that's the case then the valve clearances should be 0.020"-0.22" for both inlet an exhaust, set with cold or warm engine. The B20A is 0.016-0.018" if you do indeed have a B20A.
You are getting confused by the numbers in the manual. The numbers you quote are for setting up the cam timing, something that an engine builder may need to do. For clearances look under "Valves".
By modern standards none of these engines are "quiet". In fact quietness may mean that the exhaust valve clearances are being reduced by valve seat recession due to having no lead in the petrol. If checking the valve clearances it's a good idea to measure them all first before you start. Note the measurements and keep it for the next time you do it. That way you can catch any that are suffering.
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