Sounds like you have a decent cooling system setup that should easily keep a 350 cool. So we're looking for major problems here, not little things like a better fan blade or a different thermostat.
With the car cold, take off the radiator cap, start the car, and while the car is idling, with the radiator cap off, watch to see when it gets to operating temp (180 in your case), and you should see coolant begin flowing in the radiator. If it flows, that eliminates a few problems, like a clogged heater core, plugged water passages, or a defective water pump.
If the coolant is circulating, next check your timing. If you've set the timing to spec, try this....
Loosen the distributor clamp a little, and with the engine idling, turn the distributor to advance the timing. If the idle goes up and smooths out, turn the distributor some more. Keep going until you hear a slight miss, then back off the distributor a bit until it doesn't miss, then tighten the clamp. Why fiddle with the distributor this way? There's a possibility your harmonic balancer ring may have slipped, which will make setting the timing with a timing light impossible. So now, if moving the distributor a significant amount smoothed out the idle, you may want to see if your overheating problem continues.
If moving the distributor did not smooth out the idle, then check to see where your vacuum advance hose is plugged into. Find a carb (or manifold) port that gets full vacuum at idle, and use that one for your vacuum advance. Using full vacuum frequently solves many overheating issues.
More things to check, but try these few tips first...
