1) it has two brass nipple, one close to the LOW/High needles and another on the oposite
side. So, which one is the gas intaken? What is the other nipple for?
You will typically find that the nipple closer to the needle valves is smaller than the other one. The nipple closest to the needle valves was originally the purge port that went to a little squeeze bulb pump to suck fuel through the carb to eliminate air. This one will suck air if left open. It must be closed off
The other nipple on the opposite side is the fuel input nipple<div style="overflow: hidden; color: rgb(0, 0, 0); background-color: transparent; text-align: left; text-decoration: none; border: medium none;"></div>