Overheating problems

Ideas:

1. Clogged radiator - try performing full coolant flush, look for signs of corrosion, consider replacing with copper/brass 3-core unit;
2. Blocked radiator fins - crap tends to accumulate on the front-side of your radiator fins after awhile, so hose it out with either a garden hose, compressed air, or a soft-bristled brush ... but be careful not to use too much pressure with any method, or you'll damage the fins;
3. Thermostat installed backwards;
4. Radiator fan pushing instead of pulling air - verify that plenty of air is going the proper direction. (Fan mounted on rear side of radiator should pull air; fan mounted on front side should push.) Usually just a matter of reversing two wires, or flipping around the fan blades (some, like mine, are reversible);
5. Air dam missing - replace with OEM piece (available from places like 50resto.com or Ford), or find equivalent-sized/shaped piece from any car in a junkyard (pretty simple design - just a long, flat section of black plastic with a few spots where you can bolt it up underneath the radiator to deflect air up into it);
6. Wrong-rotation water pump installed (serpentine-belted 5.0's require REVERSE-rotation pumps);
7. Defective thermostat;
8. Possible intake/head gasket leak - check for signs of oil in water/water in oil ("milkshake") or white stains/coolant stink after motor is warm.

That's all I can think of right off hand...

a common mistake is with the thermostat. A lot of people put them in and they dont get seated in the right position. Also putting them in backwards, but i dont believe you would do that, although it has done before. If you recently drained your coolant then there still might be air in the system.

If it wasn't doing this before you swapped over to a carb. Try jacking up the drivers side front of the car, remove the radiator cap, and run it until the stat opens. It should help burp any air that may be caught in the system. You also didnt mention the condition of the radiator cap? They are cheap and often overlooked.