Beats me. Just speculating...
That serial number goes to a .38 Super built in 1963.
Perhaps Mr Monnich was the gunsmith who converted it to .38 Special.
Perhaps Mr Monnich was the customer who had it converted to .38 Special.
A search finds mention of a Monnich marked gun on one of the other gunboards in 2004.
Nobody knew who it was then, either, but it leads me to the gunsmith theory. Probably a local or regionally known shop without big name national recognition in the gunzines of the day or the www now.