Using info garnered at this website and Healey6.com, I am putting in place heat shields in my Series 1 BN7. These were all missing, and I don't think the one over the muffler ever existed. The floors had been replaced, so the usual fittings weren't present in that area, but they are in the engine bay. I have also bought a commercial woven tape and have thoroughly wrapped the exhaust pipes from the manifold to the muffler---yes, I removed the muffler and tail pipes to do this. For the record, I am using 1/4" Hardie Backer, a cement board material intended for showers, etc. It cuts and drills rather easily, and I am backing the fasteners with proper looking fender washers. Since I had free rein above the muffler, I initially cut a piece to the pattern shown on the above-mentioned web site. However, on further consideration, and noting that fastener (screw) holes did't exist on my floor, I made my shield to fill the entire underside below the driver's seat, with mortises for the exhaust hanger and seat belt bolt. On advise provided here, I also used used quarter inch thick spacers from the Hardie Backer between that shield fastners and the floor. Finally, my question. The engine bay shields, and there are several, are secured by nuts that were welded/brazed to the firewall, etc. Were those nuts intended to provide air space between the backer and the shield, or were the shields mortised so that the shield could be put hard against the surface?