The S in the AC plug number stipulates a projected tip. This was used to prevent fuel fouling at low speeds and also to cool the spark plug at higher speeds.
Thread length is the same between the 2.


BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022