There is only one 1-1/2" in the SWCA database in the 182,XXX serial number range. That 3rd Model was noted as a special order, so must have had a letter. Supica/Nahas do not state under the 3rd Model the number made but say they are quite rare, worth substantial premium.
I am guessing that the front sight was modified, but if so could easily be changed out to an original half-moon front sight. In my opinion, it would add to the appeal of the gun. Members here would have original sights if interested, just post in the Wanted to Buy section.