You shouldn't have gas sitting in the manifold. That indicates that something is wrong with the carburetor. Usually it means the float is set too high and gas is spilling out of the fuel bowl. You mentioned in the previous thread that the carburetor was rebuilt. By whom? And how long ago?
The pops and white smoke you describe are also a concern. Usually those indicate that the timing is incorrect. Before you address the carburetor, I would look into the timing. Make absolutely certain that you have the firing order correct. Then make sure that the rotor is pointing to cylinder one when it's approaching top dead center of the compression stroke.
To determine when cylinder one is approaching TDC, remove the spark plug for cylinder number one, put your finger over the open hole and turn the engine over by hand. You should feel air pushing out of the spark plug hole when the piston is approaching TDC. When cylinder one is approaching TDC, the rotor should be in the proper position to send a spark to the cylinder one spark plug.
If it is not, then the distributor has been installed incorrectly. The firing order for a Chevy six like yours is 1-5-3-6-2-4, so once you've located the cylinder one position of the rotor, the plug wires should be installed in that order in a clockwise rotation. When cylinder one is at TDC of the firing stroke, the rotor should be pointing directly toward the right fender and the number one plug wire terminal on the distributor cap should be the one farthest away from the engine block.
If the plug wires are installed in the wrong order or to the wrong cylinders or the distributor is incorrectly installed so that the rotor is at the wrong cylinder when firing, the result can be pops and white smoke.
All of this needs to be correctly done before you try to start the engine.
