I have a California built 1970 383 Air Grabber Road Runner. California cars came with Holley carbs with a vent. I believe the original Holley carb for my car should be a 4217-A, which is for a manual transmission 383 car with the C.A.S (Clean Air System).
Your car sounds like it is also a California car. If it is, then it uses a 3 port oil breather cap and has one line connected to the vapor return line, another going to the carb vent, and the third going to the air cleaner.
I have a service replacement Holley 4749-1, which is proper for the car and has the vent. My car is now fuel injected and I most likely will not return the car to stock, so I might be willing to part with the carb. It has not been used in 5 years or so, but has been in dry storage since then. I would expect it needs to be pulled apart and cleaned, although I did drain it before I stored it so you never know.
Let me know if you might be interested and then I can get pictures, etc.