What's the best method to replace cab corners?

[Tri5Nerd]

I'm ready to replace my cab corners on the 55.2, I've looked at some writeups, but am still a little confused.
When cutting the rusted corner, there seems to be some spot welds on the lower inner corner, should I drill those out before the panel will seperate?

Should I overlap the new panel or do a butt weld? I see that some overlap but the issue will be how to fix shrinkage if any from the inside corner, remember that the inner corner will still be there.

If anyone has a how to please post it.