look at the flat pad located behind the dist. the first three numbers will tell you what the engine size is.
there is no pcv valve on your truck so any gasses that are being formed (blow by) are not being sucked into the carb and burned. the road draft tube which is that pipe in front of the dist. pointing to the ground is where the smoke, fumes or what ever is sucked out of the engine when the truck is moving at a moderate speed. as its being sucked out fresh air is being drawn into the slits along with whatever is in the air (dirt, moisture) on the valve cover, that is a simple ventilation system but works as long as your moving. when you stop the vapors come out the valve cover. you can always pull your valve cover and run the engine and see whats going on under there. once i understood how the system worked i stopped worrying about it. find a 350 or larger gmc and swap over the pcv system it has over to yours. no more smoke and the air entering is now filtered.
