I have the parts laying in the shop but where to start so I don't get into trouble down the road.

Need to install new trunk floor, extensions and lower side panels (Classic Industries). Additionally have both new rear quarter panels (NOS) and rear tail panel (NOS).

What is the best chronological order to do these replacements without losing control of good fitments? Car has never been in a wreck so no issues there.

Thinking I should basically cut the "middle" of the quarters out so that I can install the trunk floor up to the existing factory quarter welds. Then remove the remainder of the quarters and install the new ones.

Looking forward to a good mentoring here... Thanks!!!

Here is my 2 cents. Don’t replace whole panels unless they are really roached. Leave as much original metal as possible and just patch the bad areas.

I would suggest doing the trunk floor first. Then the extensions and drop-offs. This way you can take a bunch of measurements before you start including a couple on the diagonal. Make measurements from what ever solid metal you have left on the original parts. Mark the measurement points on your new panels so you know you are starting out OK. I would tack weld the trunk floor and components well enough that there is no chance they will move out oof position, Then do one quarter panel at a time also tack welding. You should be ok then assuming you used the measurements and reference points from the original panels. By tack welding to get everything lined up you should be able to undo sone welds and move things if need be.