For the Number of Cylinders, there are two choices. (Note: Does not include anything bigger then 1-ton)

6

Denotes six-cylinder engine. This could be a 251 L-head six, or a 170, 198, or 225 Slant Six. Conventional pickups and A-series compacts came with slant sixes while WM-300's came with the L-head sixes.

8

Denotes a V8 engine. This could be the LA-273, A-318, LA-318 (`67-up), B-361 or the B-383.