That's an add on secondary metering plate from another carb.
The base plate was a mod to convert it to a double pumper. This carb is a true vacuum secondary carb.
Where the metering blocks came from is a mystery because this has pieces from all over. To double check the throttle bores, flip it over, remove the base plate and measure the body because the base plate may be off just enough to fool you.
This can be a very workable piece, unfortunately it's been modded to the point you are going to have to tear it down to do a "ground up" to create something to be dependable.