If you're talking about just replacing the trunk (boot) floor, I did this to my TR3. It was time consuming, but not especially difficult. I took the old panel out in sections using one of those pneumatic body saws and cut-off tools. I first cut away the center section that covers the spare tire well. Be careful not to cut into the well or the flange. Then I worked on the outer pieces. At some point, you will have to prop up the spare tire compartment so it doesn't flop down. Drill out whatever spot weld there are, and clean up all the sealing putty. There's a bunch of it at the tail end of panel, which was still soft after 45 years! Grind down any of the remaining spot welds etc, paying close attention to the spare tire well flange. It took me awhile to figure out how to get the new panel in without cutting it in pieces. It will go in, but you'll have to play with it. It took me about a half an hour to get the right angle.
I put it in the best position (it will be a compromise), and then used a few of sheet metal screws to hold it there in the flange of the spare tire well. I marked the areas where I wanted to do the plug welds, took the piece back out, and drilled the holes for the plug welds. Put the floor back in located by the sheet metal screws, and then plug weld everything in place. Remove the screws, and weld the holes shut.
Edit: IIRC, my floor (from Moss) did not come with the right angle brackets for the gas tank fiberboard liner. I just made some from some sheet metal and welded them in place.