I join my barrels by using different grades of solder with different melting, flowing points. My quater rib is brazed to the barrels as is the under lug for the forearm. By brazing these I elimanate the problem of every thing softening up as I make adjustments during regulating. I have found that a regulating wedge at the front sight position, another around where you want the swivel to be (this wedge can usually be the swivel if made correctly) and another mid way between the two makes life rather easy. I usually start with the barrels cross firing at 50 yards and by using a bore sighter, dial gauge and serface plate have found it rather easy and fun to do the regulating with out too much shooting. One thing I discovered is the reason for the middle wedge. At times you may find that if the barrels are crossing that spreading the muzzels apart is a very tricky solution as a little goes along way. If you drive the middle wedge either forward or back along the tapper of the barrels you may find it alot more forgiving.
As for the top rib, I have several cutters for my Milling machine that have cuts around their radius for cutting groves in ribs. These came from a guy who retired from Poly-Choke in Connecticut and they work great. I am talking to a shop about makeing a couple up with different LPI with a radius on them I will keep you informed. I hope I have been of some help!