Looks like NO effort was made to blend the barrel and monoblock. The lack of attention to detail here makes you wonder about the rest of the rifle...
This type of thing perpetuates the lack of understanding most of the shooting public has about double rifles. When they discuss the "cost" of double rifles, this leads one to think that using shotgun actions is standard practice. Of course, if all builders used the "one action fits all" method, they would cost less. There are good reasons why traditional makers don't do this.
I suspect the hot 405Win loads are maxing out the 20ga. action's strength too.
They should send one to London to see if it can pass proof.

Ronvella could teach these guys a thing or two about the proper method of rebarreling a shotgun as a double rifle.