My A's have the false seat belt latches under the front edge of the seat. I buckle the belt onto the false latch, then snug the belt down on the seat with a hardware variety (ABC type) extinguisher caught beneath the belt. Beware that the powdered type extinguishers can settle. They need to be rapped hard on something or on the ground to loosen the powder inside just before they are used. I've also put out an engine fire I passed by with a blanket (late 80's ish 5.0 T-bird), fellas whole ignition system, plug wires and distributor were burning. Never understood that one.