Hi Ron,
Thanks for the info.
( next time I'll use a smaller furnace at a lower temperature
)
There is no trace of any kind of sear or magazine safety ever being installed on this pistol and it's condition is good enough to tell. Which is kind of interesting.
After some extra cleaning and investigation of assorted small parts like the front toggle, the hold-open and the trigger they all have the '11' number on them. The receiver serial number is most definately 1511. Sadly no further sign of a letter suffix