Possibly through a special order since several 56 codes are correct for the Model 63. That would be very difficult to determine w/o some form of accompanying documentation. (original factory order; purchase letter; correspondence; receipt; etc., etc.)
I’ve handled Model 63’s in both rifle and carbine versions, early and late, grooved and non-grooved, but I also can’t recall seeing one with a receiver sight or tapped for one.
I did see a deluxe 03 with receiver sight not too far back in years. I assumed it was an after-market application… maybe not?
Interesting question. Maybe someone else will chime in.