The OP definitely states 650B.
It wouldn't hurt to verify, but I think at this point one should take his word for it.
One "standard" on modern bikes is that if the tires use a fractional inch PLUS a decimal width, then for at least the larger wheels, they will generally be 559 (26" MTB), 584 (650B, 27.5), or 622 (700c, 28", 29").
If it has a fractional inch diameter plus a fractional inch width, then it will be some vintage oddball.
It sounds like there are a few options for road 650b, but none of them are particularly narrow.