First slant, multiple questions

ok all. I got a smokin deal on my first Mopar (I’ve been more of a Jeep guy). I know nothing of the slants but am learning. I picked up a 69 four door dart custom the other day. It is hard starting, and would die every time you shifted gears (auto trans , from forward to reverse). The car immediately lights if you prime it with a little gas doe. The throat.
I cleaned up the engine bay a little bit today. And fed it some carb cleaner while it was running. It now will stay running when changing gears but will still stumble as you start to accelerate. I discovered:
It leaks a lot where the red arrow is
The green arrow is an unused port?
This is a later Holley “economiser” carb?
Am I correct in assuming it’s a later Holley 1920 or a 1945?
More pics below

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