What's really odd is the electric choke which Nissan started using around '71. There is no provision for a BCDD which started about the same time but there are two vacuum ports on the carb base... one for vacuum advance and presumably the other for EGR? This would indicate (sort of) a carb from the early '70s but I can't find anything in the late '60/early '70s even close. Most were Hitachi. A J15 was used in the Mexican 710 and export Nissan forklifts, replaced by an A14 '74-'78? A J13 for Mexican built Bluebirds. Maybe from something like the J18  used in Mexico and farther south?

I've seen these Nikki carbs on early 70 chevy luv trucks. It's got a gas return outlet, interesting. I'll have to check my chevy luv trk manual. I'll let you know if it's in it.  

I have this exact same carburetor on my 521 I got in Mexico that has a L20 swap in it. I am also trying to figure what carb it is and how to adjust the air fuel mixture and what kit to buy to rebuild it.

Only the idle mixture can be adjusted. The overall running mixture is set by replacing the primary jet with larger (richer) or smaller. (leaner) Larger at sea level and smaller as you go higher in altitude. Generally it will run good enough with any jet that is in it.

Hmm so I bought this in chihuahua, chihuahua which is at 4k feet and I leave in Dallas which is zero and the truck runs rough. How do I find the jets for this carburetor?

Rough could be anything. Slightly lean would run fine just lack power and mileage. My 710 came from 5K and I am literally on the ocean. It had 99s in it and I went to 112. Power picked up and so did the mileage but it ran just fine.

  Pull yours out and the size is stamped on it. I bought about 20 metric jets off Amazon (a few $$s) for tuning a motorcycle. They come in a range of sizes. If it was set for 4k and you are basically at sea level then it's would be running slightly lean so a larger jet is needed for the extra air. For example if running a 99 jet try a 103 or more.