Sounds like you have enough room to adjust for convergance. There a lot of things to consider though. Are your barrels soft soldered or brazed? What is your skill level with soldering/brazing and machining ability. What equipment do you have access to. Separating and rejoining side by side barrels is not as simple as it may appear.
It still seems to me that dropping 1/8 to 1/4Oz in projectile weight would be the simpler thing to try first. YMMV