Aaron,
Some interesting observations. There is no denying the concentration of stresses at the apex of a 90 degree joint. However that's a fault common to every gun that was ever either sleeved or built on the mono-block system. One thing that I have going for me is that this is a bottleneck cartridge with a fair amount of body taper. About 1/2" before that seam, the diameter of the cartridge drops from the .468" at the base down to only .294" at the neck and then .264" at the seam, the point of the highest stress. This provides a lot of extra steel at that point. As I said earlier, proof firing in a couple of weeks will show whether this project was ill-advised or not.