More than 201?

[Keith Seymore]

Here's how it appears on a truck SPID from the era.

In this case the engine is an L47, with an ECL of "20" (whatever that means, as you say).

The ECL describes additional detail beyond the RPO, defining proliferation for that component. For an engine, it might define AC vs None, multiple carb vs single, manual trans vs auto, California vs Federal emissions, etc. For a rear axle, it would define ratio, locking vs open, perhaps special brake friction material, etc.

So while we know what the ECL does - we don't necessarily have the secret decoder ring.

K