Murph,
I think we'll find that the 'normal' process is to have the tube extend thru the monoblock. I think it can be made to work fairly easily either way. Protruding to the breach requires second op to clean up the face, tubing to a step preserves the face but requires holding a close tolerance when machining of the stepped hole depth and the length of the turned barrel tube and requires something to be done with the potential for moisture penetration in the gap (if not soldered). Soldering has some advantages.