If you go order directly from Rei, those can be modified to something better which is the good part. Although, I can imagine if he ever gets more buys from retailers, the bespoke/semibespoke aspect thing may disappear or may take longer or more expensive.
Yeah 45cm is around size 50 unless you have to wear this really low waisted which would look weird. But from what has been mentioned here, l-0 fits very generous on the top block but becomes really tight on the calves/leg opening. So probably that's where it will fit a size 46.