For anyone else doing this I thought I'd post a pic of the fastback with the new floor pans and underside almost done. I did the overlap type install on my new floor pans and then welded above and below. Not perfect but not bad for a rookie. I then cleaned off all of the old undercoat etc from underneath and brushed it with POR-15 semi-gloss black. Once the POR-15 had cured I topped it with something called Pro-Form European Texture GravlGuard which is very tough stuff. I'm now going to seam seal everything and re-install the rear end which was also re-finished. I'm putting in new GAT 4.5 mid-eye leaf springs and all new brake components on the rear drums. Hopefully the rear sits at a good height with these springs.