The fuel vapor line is not absolutely necessary but since you are replacing your pump, it would be a good time to get it right. The fuel vapor return does several things including letting trapped fuel vapor return to tank. Also, it helps keep your fuel cool by keeping it circulating.
The line connects to the pump.
When you go to the auto parts to buy the pump tell them you have a 69 Firebird with a 400 4 barrel and they should give you the right pump. If it doesn't have the extra connection for the vapor line get them to look further or go to a different parts store.
