Bolt in cage?

It's really the headliner I am worried about.
I used to build totaled cars back in the day, and I have pulled more than my fair share of interiors.
And seen the damage an errant spark that gets past the covered up upholstery can do.
Thats why I wondered if anyone had tried to do the mock up in the car, cut and mark everything then weld it together outside and with maybe just the seats out and windows down slide it in the open door and stand it up inside?
Like a ship in a bottle!!
Post#5?...