[OrrieG]

Bipass the heater core and check the hoses to it for blockage, that could be your part of your over heating issue. Sooty plugs is carb jetting issue, choke is staying partially shut making the mixture too rich or timing (fuel not getting completely burned). Yes I know you got a new carb, but that does not mean it was tuned for your engine. Backfiring thru carb AND exhaust means your timing is jumping from advance (carb) to retarded (exhaust). This will also affect the engine temp., retarded timing causes temperature to got up.