Curl,
Good point about "true monoblocks".
If I was intending to build a double for serious use as opposed to casual use and build it for a serious cartridge which developed high pressure and intended to use a shotgun action, I would insist on a true monoblock and would not consider using a cut up set of barrels.
I would also want the barrels to be silver soldered to the monoblock.

If on the other hand i had a shotgun action which i wanted to build into a double rifle, and that shottie used dovetail or chopper lumps, i would not want to use a high pressure cartridge.
To avoid any risk of melting the dovetail or chopper lump join i would use high temp solder to join the barrels to the "untrue monoblock".
Force 44 Hi Temp or equivelant would be my choice and then the rest of the barrel assembley could be done in force 44 without risk of melting any of the barrel to u-t mono to lump joins.

I own 3 doubles built on shottie actions and all three use true monoblocks and all three use silver solder at the mono barrel join.

Also a good point about Beretta.
Cheers