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Yes, the Nissan A.I.S. system operates similar to the air pump system except is uses harmonic pulses to inject the air.

Same caution applies.

When I had a " stock" carb I just pulled the plunger out. I personally never had any sort of problem.

Your call.

My 77 GFU "special carb, plugs, electronic ignition, Cat converter. Doesn't have an air pump. It has an air pulse from on top of the thermo to the side of air cleaner.

If you remove the anti-backfire valve, the risk is getting a backfire, and in worst case an engine fire. The anti-backfire valve is part of the air pump system, so you would have to remove it as a system and not the valve alone.

is that the bronzy looking large hex nut on the carby with a wire attached? if it's that then the bum way of dealing with it if you don't have it is or it's not working is to stall the car when you shut it off. Can't say it does you bearings any good though

Any thoughts on the anti-backfire valve?

Is it necessary? What problems would it cause to disconnect it? What problems arise from a mal-functioning ABV? Would it be worth putting a new one on?

All of the parts are getting tired, I am not sure which items are going to make my 77 run smooth thru idle to freeway.