well, Ministeriali is the plural, you have a " Ministeriale" model ! :bluewink:
Your Grassi 4 digits is a very early horn (in Grassi terms) just about 1961-2 (these first few serial numbers are, like the last ones, a bit hazy since in my chart there are gross approximations )-
I am not familiar with that particular shop in Naples ( I know Miletti, Cerutti, Quaglia, Loveri) but in Italy like in France, many shops used to have their instruments custom branded with their own names . Most of the shops were and still are located around the conservatory , San Pietro a Majella , in the via San Sebastiano.
The marching band market vas huge at one time in Italy and every small town had , at least , one. Quality would vary greatly and so was the quality of the instruments that were required for this mostly simple music rarely requiring any virtuoso performance if not the one of a soloist or two (if the band was fortunate enough to find one among the villagers).