Hi Timmaaaaay!!!,
There are no model numbers on the carburetors, just KEIHIN Japan. I think these are the stock carbs for the 71 CB 500, but who knows what happened to the machine in the last 45 years. The throat diameter on the engine side is 27mm and 35mm on the choke side. These measurements were made with a cheap plastic caliper so they night be a mm off.
Thanks,
John