Ken,
I think you've chosen well with the monoblock design. It should allow for precise machining of the dollshead if that feature is included.

Did you mean that the breachface of the monoblock and barrel tubes would also be laser welded? If not, some method of sealing the joint at the tube/monoblock on the breachfaces should be considered to prevent moisture intrusion.

A parting thought: Did you and Steve consider threading the barrels into the monoblock like a rifle?