I just installed a 32 mm mikuni on my '73 125. I ordered the bing fiber bushing from Al Buehner then machined the inner diameter to accept the bushing then cut four slots with a hacksaw so I could clamp it on stock cylinder spigot with stock bing clamp. The air intake boot stretched enough to fit over the mikuni just fine. The stock cable worked just fine. As far as jetting goes, it came with a 200 main and a 35 pilot and at sea level seems to work amazingly well.
Don
Don