My '66 Charger is the same way. I used some 1" angle like Doug and a lap belt from a 68 Plymouth. The aluminum box '67 has is nice and looks to be three pieces.
On the subject of batteries internally collapsing - has anyone had to heard of this happening in the last 10 years?
I had a friend have one act up on him due to this. It worked intermittently, sometimes it would start, sometimes it wouldn't. I don't think its a common problem but its worth consideration when you set the car up. This only applies to a conventional lead acid battery. It doesn't matter for any kind of AGM product like Optima or Odyssey etc.
