jeremy,
This is mysterious. The cooling system would normally go sour gradually unless there was a drastic jump in the outside air temp and it couldn't overcome it. A sudden heating problem would indicate a mechanical change or problem with the engine proper. Too much advance timing will cause heating but usually involves pinging which might be heard.
You worked on the carburetor and replaced a vacuum advance line...could the vacuum line have been reconnected to the wrong port and the distributor is seeing vacuum all the time.
Check your coolant level, fan belt tension and radiator for loose shop rags that might have covered it...if this was cause and effect, the cause is in there waiting to be found.
Stuart
