I was thinking that too, half an inch lower BB and the stays are within 3mm in 18″.
Wheels I’m not so bothered about, rims are cheep and I can build them myself. Tyres are consumable, if I didn’t need new ones alreasy, I would in 6 months, so new ones aer no big deal. But forks are relatively expensive and last a fair while. Suppose you could put a 650b rear wheel in there, and run the forks at 150mm, then it’d be the same as 650b at 130-140mm. Like Faust, I’d be more interested in the big headtube than anything else.
45650bC, with 30.9 seatube and a 44mm headtube would have me reaching for the credit card though!