[LMH]

On a standard Auotlite street car, there's a little more on the firewall. Pictured in Glens photo above is the Lucas DB10 relay next to the heater hose. Above the drivers footbox (not pictured above) is the three wiring harness plugs. They are held in place by a lip on each plug. There are four nuts visible on the firewall side, that I think hold the heater in place. I don't know off hand what sort of fastener is used to hold the wiring harness in place, I'd have to check. Of course, there's a hole for the wiper drive tube, the heater hoses and footbox vent control cables.
The FIA cars are different though and probably different from each other as far as appearance. Kind of depends on what you're trying to replicate.
Larry