You need ALL PB(Beretta) or BMR/BMB(Breda) parts for EACH rifle with NO admixtures allowed.
A Beretta
M1
will have ALL PB marked parts and a Breda will have ALL BMR/BMB marked parts.Everything except screws and springs and sling swivels(stacking swivels too) and Breda rear sight ELEVATION knobs were marked(PB knobs WERE marked)
Firing pins and extractors ARE also marked as are rear sight apertures.
Assembling the parts to do a build IS lots of fun and not too expensive IF you are patient.You see receivers and non matching rifles quite regularly so buying a barrelled receiver might be the way to start.
The fit and finish on the
Italian
built rifles is easily the equal of H&R's and late 5 and 6 million SA's too so you WILL wind up with a lovely rifle IF you perservere.
Cheers,
John R.