Also tightened loose breather pipe from rocker cover to carb, don't know what this is supposed to do
In theory it helps to pull clean air through the crank case - this helps to remove any moisture from places it shouldn't be and reduce condensation in cold weather.
In reality a worn A-series will have a +ve pressure in the crank case (due to the piston rings leaking a bit) so the air will be finding a way out of the breather with or without any light suction from the air filter or carb.
A viable alternative when there is crank case pressure is just to vent the breather to atmosphere.
Anyway - I'm glad to hear your issues are gone - I've heard of people having problems with these radiator covers. I've never been keen on them as the thermostat is responsible for keeping the engine warm and the radiator is responsible for providing as much cool water (back in to the engine) as the thermostat allows. If the radiator returns hot water, then the engine can just get hotter and hotter.
If the engine is hot enough, you should have a decent hot water flow to the interior heater. If it gets any hotter, the thermostat opens to allow it to cool a bit. In really cold conditions the thermostat will spend a lot of time closed. On modern cars at below -10°C it's often the case that the interior heater can draw more heat than the engine provides. I've had thios on a few cars where the interior heater on full blast with windiows open reduces the engine temp below normal operating point (i.e. the thermostat is fully shut and the main radiator has no flow)
If the water pump is good, the heater matrix isn't furred up or blocked, and ther thermostat is doing what it should, then you should get enough flow to the minor's heater. all these things are worth checking if your heater output is very poor.
The only further limitation will then be the temp of the air passing into the heater. If it is being fed very cold air, it won't heat it up to a decent temperature - hence the modification to remove the cold air inlet.