As Dilbert and I previously stated, there are many things that can cause this. Need to go back over everything from square one and check everything carefully. Odds are something is binding or not hooked up properly and since we aren't there, we can't see the issue.

Turn the carbs over and look to see if the throttle blades are closed fully. If not, back out base idle screw to see if throttle plates close. Look for signs of the throttle blades rubbing in the throttle body. Push the throttle shafts side-to-side and feel for play and any binding while opening/closing the throttles.

If the throttle blades are not fully closed, you need to see what is binding (linkage, throttle plates, fast idle cam, etc.) and causing the throttle to hang open.

Then move on to check the carbs as they get installed...

Do the base gaskets show signs of rubbing anywhere? How about on the edges of the throttle bores in the intake?
It doesn't take much...

Then I would reinstall the carbs loosely and open the throttle bores to make sure they move smoothly and are centered in the bores. Tighten the mounting bolts a little at a time to specification and recheck the throttle for any binding. Repeat on the next carb. Reconnect/adjust the carb-to-carb linkage. Is the throttle return spring weak, not returning the throttle to closed position?

Reattach the throttle cable and kickdown linkage, making sure they don't hold the throttle open. Reconnect all the fuel and vacuum lines.

Check the PVC and power brake booster hoses. Maybe one got damaged during carb removal/installation. Also check to PCV valve to see if it is stuck open. Shake it, does it rattle. You're basically looking for anything that would cause a large vacuum leak. Once running, disconnect the brake booster and plug the line to see if the booster is bad.

Did you move/bump the distributor when removing/installing the carbs?

Do you still have points or has the car been updated to electronic ignition? If still points, check the dwell to ensure it has not changed. Reset as necessary. Check the mechanical advance in the distributor. Pop the cap and check to see if the mechanical advance return properly by rotating the distributor rotor and release it. The rotor should "snap back" into it's original position. Repair as needed.

Start the car.

Once warmed up:
Check the base ignition timing. Is there any vacuum going to the vacuum advance while at idle. If there is, the throttle is open too far or the hoses are connected improperly.

Turn car off.

Good luck. Keep us posted...