Holley vent whistles

[Woodz428]

To begin with the vent piece of brass you describe is the standard
vent plate. The plastic "whistles" are supposed to prevent fuel from sloshing out vent tubes under hard G forces (cornering,braking and acceleration). I would say thatthey should be installed if you plan on such activities. It makes me curious about the metering blocks. Since the whistle tubes require a small brass rivet to hold them in place, they either left the hole unplugged, plugged it with the regular rivet(minus vent) or swapped metering blocks all together. I would personally suspect the latter since I've never had to remove a whistle to do any carb work. You can look at the metering block and determine if they were ever used with a whistle because of the mentioned rivet/hole.