[Grady Clay]

Juan,

In addition to a cranking compression test, I would measure the actual cam timing and check the valve adjust on both sides.

Are all six throttles sitting on their stops? Same when you connect the linkage?
Do they come off the stops at the same time?
Is there any radial play in the cross shaft? (Missing bearing?)
Are the idle air passages in the throttle bodies clean?
Does it appear as if the throttle bodies are different from each other?
Are there air leaks between the throttle body and head? Between throttle bodies and stacks?
Is the vacuum retard connected? Leaking?
Are the six cold start nozzles in place? Hose connected?

You can check to see which side is lean by popping a rod off one side and slightly opening that throttle with the center linkage. The side that is more lean will pop and slow, the richer side will speed up.

Any chance it could have different cams L-R?
Do all the heads have close to the same casting date?
Are the heat exchangers the same?
What kind of muffler?
What do the plugs look like L-R?

Best,
Grady