however i believe they are temp sensor bungs, not 02 sniffer bungs. 02 sniffer is i believe an 18mm thread.
I still have the stock exhaust with individual bungs. I got a bolt like the one installed in it, drilled through the center, and attached a copper lead tube to it. I can then attach the small rubber tube from there (without melting it) to the tip of my sniffer.
I can only set one cylinder at a time, and this is very time consuming to do. I've always considered building a small brass cylinder device where I could have 4 small valves, attach all 4 cylinders to the device while the bike exhaust is still cool, and only reach under and select which cylinder to set with the flip of the right valve accordingly. The way I currently do it, the bike is kinda hot from setting the first carb when I have to disconnect my small homemade adapter to move it to the next cylinder.
IMO, this process is so time consuming that I don't do it very often. Lately, I have gotten just as good results, if i lower the idle rpm's enough to just keep it running, I tweek the air/fuel screw one at a time and get OK results. (I call this "doing it by ear".)