Cowlitz is talking about engine names. As everyone is aware of by now 366 cu.in. roughly equals 6.0 liters. The 366 is a completely different engine then the 6.0 LS based small block that came out in the 90's.
However, in order to avoid confusion when talking about chevrolet engines, most people will refer to the 366 as the 366 and the 6.0 small block as the 6.0 regardless of what kind of tag is affixed to the engine.