Larry;
What I refer to as conventional is the underlump just fit up into an angle cut into each bbl & brazed In. Just think of fitting the lump up into the fork of an upside down V. The dovetail joint is basically the same except the cut stops short leaving a step. If you tryed to pull the lump away from the bbls the dovetail has some actual metal-to-metal resistance, while the conventional has only the strength of the brazing. On a top bolted gun there is little stress trying to pull the underlug away from the bbls so the extra fitting etc of the dovetail joint is not really justified. I went & checked the joint on my 1890's era J P Clabrough with double underbolts & a doll's head. It has the simple V lines of a conventional joint but is still holding on strong.
