As mentioned before, the two door conversion that we executed was made possible from a '63 Plymouth B-body donor. The problem is that the vent widow angle is different than the '64/'65 cars so we needed to remedy this.
Here's the original angle issue.
After hanging the door in it's new habitat with reasonable door gaps so it doesn't look completely cobbled together we began the surgery. First plan of attack was to remove all of the guts from the door including the vent widow assy. It was decided that a straight up door frame graft was our best option since the spot welds attaching the frame to the door is quite complicated and in depth. The cut on the lower portion could be made about 3"-4" up from the main body of the door and still maintain the new angle that we will introduce.
The pieces to be fused in were graciously donated to us by our old 4dr doors. Lining up the new corresponding pieces was fairly easy with the door in place and gave us a good reference point with the top of the door frame. With the new section tacked in place we could remove the door and finish welding it on the bench.