Tallchief, if you're still having trouble getting the barrels to shoot together, you could cobble up a variation on my old self-alternating rear sight:

http://www.google.com/patents/about?id=1Hw1AAAAEBAJ&dq=3404598&ie=ISO-8859-1

It's well out of patent now, of course, and would be a bit of work to make as a one off. If one barrel shoots higher the other you could get a forward-tipping folding-leaf sight, set the higher leaf for the lower-shooting barrel, lighten the spring in it and epoxy a couple of little lead weights high on the front. Then, when you fire, the inertia under recoil should drop that sight down, leaving you to sight over a lower leaf (set for the other barrel) with no weights to pull it down.

Not spiffing enough for the purist, of course, but it does work.

- Paul