S/R=Short reach spark plug.
L/R= Long reach spark plug.
N/D= Narrow deck (.255 thick).
N/S= Narrow deck with spot faced flange holes.
N/X=Narrow deck with 20 barrel cooling fins vs normal 18.
W/D=Wide deck (.410 thick--bolt hole pattern different from narrow deck flanged barrels).
T/W/D=Thin-wide deck (same bolt pattern as wide deck, but only .355 thick)
W/D/X=Wide deck with 17 cooling fins vs. normal 18--541 barrel
AE= Aerobatic engine.
I= Fuel injected.
L= Left hand rotation crankshaft.
O= Opposed cylinders.
0-360 A1A, A1AD, A1D, A1F, A1F6, A1G, A1G6, A1G6D, A1H, A1LD, A2A, A2D, A2F, A2G, A2H, A3A, A3AD, A3D, A4A, A4AD, A4D, A4G, A4J, A4JD, A4K, A4M, A4N, A5AD, C1A, C1C, C1E, C1F, C1G, C2A, C2B, C2C, C2D, C2F, C2E, F1A6, G1A6