I am in the process of replacing both full rear quarters and the left and right trunk floor pieces. Which should I do first? and any suggestions on the process of replacing the trunk floor parts. And at what time should I replace the filler panel between the trunk lid and the rear window? All the parts are new goodmark stuff. Any reply would be great. The car I am working on is a 70ss.

You should weld in the new trunk sections first, then cut off the 1/4 at the body line, and weld the 1/4 to trunk lid extentions in. Trim the old 1/4 and install the new one.

I second that motion. Trunk FRIST ;)