Finally, I have painted the plane and I am installing the fiberfrax and "fire stop"type caulking(3M Fire Barrier sealant-red-four hour rating) and metal firewall.
Marc and several others posted on the FW fire resistance of using SS/fiberfrax, instead of aluminum/fiberfrax.  
Let's look at the layers and physical limitations on:
1. SS/fiberfrax
(Stainless steel has a higher melting point and a lower temperature conduction, than alum.)
SS-fiberfrax(with Hi temp OF-180 "white glue")-glassed foam-glassed plywood

2.Alum/3M Fire Barrier/fiberfrax
Alum.-3M Fire Barrier-fiberfrax-3M Fire Barrier-glassed foam-glassed plywood
In the event of an engine fire, there are several stages to consider.
Early on, there may be combustion of oil from a pressured hose leak or combustion of  fuel from a pressurized fuel line. Next, the engine is switched off and the fuel valve is closed. If the engine is not switched off, then the insulation for the fuel injector wires will melt and break the circuit and then the engine will be out of service. The fiberglass cowling is a major source of burn material. I have done burn test on layups without foam and as a result of those test, I choose to use a low burn plastic for my electrical channels. The canopy will burn very fast and that is what will raise the heat in the engine compartment until there is burn through of the canopy. I do not have any idea of the time frame for that process, but the FW has to hold up until then, or the CS is going to fail.
What will resist the heat transfer to the CS and engine mount reinforcements?
The addition of 3M Fire barrier sealant on both sides of the Fiberfrax should add enough resistance to heat transfer, even if the alumuminum melts in some places. All holes in the FW are sealed with the 3M product, especially the electrical conduit holes (forward of the end of the rudder cables, so as to not coat the cables). I do not see the AS "white glue" as adding much heat resistance to the fiberfrax. Adhesion of the fiberfrax to the FW is paramount in preventing a burnthrough on the FW. I have a secondary FW cover on the interior of the cockpit.