And yer welcome 64phil.
When you print the templates, turn off page scaling. I know you can do this if printing from Firefox web browser.
Oh, and the templates are made as if your head is in the wheel-well with the brake drum and your looking at the "filler".
As for your question about making it all out of one piece, I think you could probably do that, but I think it may actually be harder because the whole 1 piece patch will have to be just about perfect. Making your wheel well piece and filler piece separate will allow some room for adjustment. When I made up my pieces I aligned all the stuff up carefully, clamped it in place temporarily, made marks with a magic marker and took it apart, welded it up out of the car, then installed and it fit beautifully.
You do have a pesky problem in having the body off the frame and the body mount brace (trunk brace) not installed. I think you'll just have to make a million measurements so the braces don't get welded in out of place. I'm thinking the rear-most body mounts at the rear of the trunk could be used as references to place your trunk brace body mount parts. Use a frame chart for measurements such as can be found in the Zazarine GTO resto guide, or the service manuals have frame measurements too.