You don't make things easy.

Gasoline at throttle plate, needle and seat not shutting fuel off completely ie float level set too high.

The smoke from the engine is black indicating burning to rich (float level) or whitish blue, indicating burning oil. Don't adjust carb by the smoke. Adjust carb for idle mixture, which may not be possible if float is not set correctly.

HEI distributors are excellent distributors and recommended. Unfortunately HEI distributors are setup for smog compliance, which means generally not having the advance of your original distributor therefore lack of power on acceleration.

Engine mileage could be anything considering the age of the truck. Doing a compression check will give you an idea of condition the top end of the motors is in.

First straighten out the carb.

Larry

I don't own a vehicle that isn't old enough to drink.