Whats REALLY strange is that both AutoZone and Advance Auto Parts show the Champion 842 and the Autolite 303 as the right plugs.. but they're two entirelly different plugs (the AL 303 are "full size" plugs)
I checked the numbers on the engine (pad to the lower left of the distributor) and the prefix suggests the engine is the original, or at least a 1946 model, 216 engine.
It would be interesting to find out how common those little plugs were, and what their reasoning was for using them.
Champions website lists the following vehicles for "applications" for the 842 spark plug..
CHEVROLET FLEETLINE (1948) 3.6LL6
CHEVROLET FLEETLINE (1947) 3.6LL6
CHEVROLET FLEETLINE (1946) 3.6LL6
CHEVROLET FLEETMASTER (1948) 3.6LL6
CHEVROLET FLEETMASTER (1947) 3.6LL6
CHEVROLET FLEETMASTER (1946) 3.6LL6
CHEVROLET STYLEMASTER SERIES (1948) 3.6LL6
CHEVROLET STYLEMASTER SERIES (1947) 3.6LL6
CHEVROLET STYLEMASTER SERIES (1946) 3.6LL6
CHEVROLET TRUCK (1948) 3.5LL6
CHEVROLET TRUCK (1947) 3.5LL6
CHEVROLET TRUCK (1946) 3.5LL6
CHEVROLET TRUCK (1945) 3.5LL6
CHEVROLET TRUCK (1944) 3.5LL6
CHEVROLET TRUCK (1943) 3.5LL6
CHEVROLET TRUCK (1942) 3.5LL6
