That is the accelerator pump.
It squirts the fuel when you step on the gas.
The nipple you cut off would have just extended through the housing to be pushed by the arm.
The epoxy should be fine since there is no fuel on that side.
The 21xx series carbs are some of the best 2 barrels made.
They're simple, cheap and dependable.
If you wanted performance, you could get a 500CFM or even a 650 CFM two barrel Holley, but with the
constraints in the stock cast iron intake 500cfm would be fine.
The 21xx had two different CFM ratings. I forget what they are now.
One for 289/302 engines, and a larger one for the 351M/W/C and 400 Engines, They even made a 429 with the same
2150 two barrel on it.
I'll be adding a 2150 to my CJ5 258 this week.
The Carter BBD is a POS at best.