When i drove my 68 from CA to Ohio, I got pulled over by 3 cops in 3 different states. (CA, NV, and CO) Anyway, one of the cops opened the passenger door to talk to me and it was the last time that door opened for awhile. The latch post sheet metal gave out during the trip and the door was jammed closed. Had to open it from the backside with the quarter panel interior trim removed. I can't remember exactly how I did it but I think I cut around the post from the back.
The thin sheet metal FATIGUES over time because the weight of the door rides on the post. The door and post should probably should be adjusted so it doesn't ride on the post so much.
If you just weld the missing piece back in place and grind flush, it'll probably happen again. If not to you then your son in 40 years.
I drilled the spot welds out of the Ohio-shaped cage that holds the floating nut inside the quarter, welded a larger second plate on the back side of the pillar, then re-welded the cage back into place. Now I have an overlapping double thickness of metal that should last for a long time. Did it to both doors.
You might consider that.
But, good work on the car so far. I bet your son thinks it's his! :D
