That's a tricky # R54910 ... only place it fits into the crack is in 1949: 11/03 ------------------ F309648 ---------------- S312650
But even there is just a shot in the dark. Otherwise, I think, It does not look like U could trust that nice looking crank to match the rusty frame. So, potentially, the only option is, at best, to be a somewhat random run off number in the end of the 1952 series or a very low volume, virtually unheard of, hidden in 49.