What were the factory original spark plugs in 1941? My Chilton manual lists applicable plugs as: Champion J-11, A.C. 45, Auto-Lite A-9, Blue Crown M-9.
Are exact duplicates of the original plugs available or have they by updated by the manufacturer?
The chart in the August 2002 issue of Skinned Knuckles show 1941 as equipped with Auto-Lite A7 plugs.
For what it is worth here is the other pre-WW2 L-6 plug listings from that chart:
1933 (PC, PD) and 1934 (PE, PF, PG) used AC S9 plugs.
1935 (PJ) and 1936 (P1, P2) used AC K9 plugs.
1937 (P3, P4), 1938 P5 and 1939 P7 used Champion J11 plugs.
1938 P6 and 1939 P8 used Auto-Lite A7 plugs.
1940 (P9, P10) used Auto-Lite A7B plugs.
1941 (P11, P12) and 1942 (P14) used Auto-Lite A7 plugs.
The original chart republished by Skinned Knuckles was published by McQuay-Norris in 1952.