Craig,
Jim Carter and Obsolete Chevrolet and others do sell the correct vacuum advance mechanism for a truck. I got a correct one from both Jim Carter (after 6 months) and Obsolete Chevrolet (on week) last summer.
The angles on the automobile advance mechanism are, just as you describe, incorrect and will not bolt-on properly/easily (on a truck).
Here is the truck
vacuum advance. Here is Chevy Duty's
photo of the truck mechanism. I will try to find a photo of the automobile vacuum advance.
Tim
