I wound up using Gunk to loosen up the sludge. I also soaked the rocker arm assembly in gasoline and cleaned the parts with a wire brush. Messy job and a lot of cleaning up but it looks much better. Here is a picture of the gummed-up rockers:

[IMG]http://i7.photobucket.com/albums/y261/bohon/56%20Chevy%20truck/Rockercleaning002.jpg[/IMG]

Here is the engine after cleaning:

[IMG]http://i7.photobucket.com/albums/y261/bohon/56%20Chevy%20truck/Rockercleaning010.jpg[/IMG]

1956 Chevy 3200