side impact protection question

[Tigger]

got a 69 and i know the doors are just a shell. what year did they start the door reinforcements. can a 69 door shell be beefed up or just put in a basic roll cage. I know the door jambs would need reinforcement also. Pics would be nice if someone has done this. thanks.

[06Daytona]

I believe with Cudas and Challengers they beefed up the doors in 72, before that they were just shells.