I was first sold on fire extinguishers years ago when I drove by a nice new pick up truck on my way home - it had just pulled over due to smoke coming out of the hood, and the two guys in the truck had just popped the hood and there was a little carb fire going. I asked them if I could help, we all seemed to agree I could not do much more than call the fire department for them as they pondered how to get the fire out. I went home, called the fire dept. and came back about 5 mins later - the entire truck was now fully engulfed in flames, cab included. Total loss.
Mounted fire extinguishers in my truck and in my girlfriend's (now my wife) SUV the very next day.
As for putting out a fire in a collector car where every piece of the engine is perfect and valuable, I strong urge you all to invest in a Halon extinguisher - a regualr "white powder" extinguisher will put the fire out and save your corvette, but it will make a real mess of your engine, valve covers, anything else metal too.