Changing out trunk pan

You didn't mention what body style you are working on. If a FB, you may not be able to replace it in one piece because the trunk opening is so small. I'm guessing the sequence on the factory line was the trunk floor was welded in before the upper structure, including quarters. However if the quarter(s) is off you should be able to get it in there.

Valiantwagon had the advantage of a big opening to work tbrough. I did front floors on my 69 but never a trunk floor.