I wouldn't say weird, just different. 1980 was the 1st year for the BS34s but they still used a brass float like the previous BS38s. It was the only year the BS34s had a brass float. All later models used the plastic float. Spec is 27.3mm for the brass float only. If you install plastic ones, they need to be set to the plastic float spec of 22mm.
Now, whether this will work or not is open to debate. Technically it should but if the plastic floats are cheap repops without the shim sleeve in the pivot, they may not work. They are a sloppy fit on the pivot pin without the shim and jiggle all around, metering the fuel very imprecisely (or not at all). My buddy had a set of the junk ones. One day, the carbs were fine, next day they pissed gas all over the place, next day they'd be fine again. He finally broke down and bought genuine replacements from Yamaha, expensive but he hasn't had a problem since.
