This Beretta Scope Base is only listed as being compatible with the A400 Xtreme, A391 Xtrema, A304 and A303 Beretta shotguns.
The Beretta Scope Base For A400/A391 Xtrema 2 Shotguns mounts to the receiver cut outs. If you have a model that is drilled and tapped you will need a different base. The base at the link below will work.
https://www.opticsplanet.com/beretta-scope-mount-base-for-beretta-1301-competition-black.html
This will work with that firearm.
From what I can tell the A390 does not have the receiver cut outs for this mount. These are the fit notes listed by Beretta: "Fits A400 Xtreme, A391 Xtrema, A304 and A303 Beretta shotguns.
Works on the A400 Xplor Action shotguns that come with the “half moon” cutouts on the receiver."
That will depend on whether or not your 350 has the half-moon cutouts on top of the receiver. This is the information provided by Beretta:
Fits A400 Xtreme, A391 Xtrema, A304 and A303 Beretta shotguns.
Works on the A400 Xplor Action shotguns that come with the “half moon” cutouts on the receiver.
According to Beretta, no.
The B-Square 16175 has been used successfully on the A300:
https://www.opticsplanet.com/b-square-shotgun-universal-cantilever-mounts-includes-1-rings-ribs-up-to-3-8-blue-161.html
Mark H.