The coolant for the carbs goes into one side (which youve already done) and the pipe on the opposite side with the bubble type thing plugs into the back of the engine block, theres a spigot in between cylinders 1 and 2
The one on top of the expansion bottle just routes down behind it and points to the floor. Its an onverflow pipe so is meant to let coolant out if the thing overheats.
Still dont know what 4" pipe your on about next to the water pump is. Cant see anything like in my pics of mine.